The MBS only flag was not taken into account when checking macroblock dimensions.
Also removes the unneeded check in init_dimensions for slices.

In order to be able to make SPS const in H264ParamSets,
modify decode_scaling_matrices so that it returns if the scaling
matrix are present in the SPS, instead of altering the input SPS
structure.

* commit '39ab2ea5':
  h264: rename mmco_index to nb_mmco
Merged-by: Clément Bœsch <u@pkh.me>

* commit '7ab5d577':
  h264: move initializing the slice start out of h264_slice_header_parse()
Merged-by: Clément Bœsch <u@pkh.me>

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

This fixes an accidental ABI break introduced at 8688d3af.

* commit '4cec43a9':
  h264: move calculating the POC out of h264_slice_header_parse()
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '6dd996c7':
  h264: move building the reference list out of h264_slice_header_parse()
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '0bad2543':
  h264: move initing the implicit pred weight table out of h264_slice_header_parse()
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit 'ed9a20eb':
  h264: split reading the ref list modifications and actually building the ref list

ref_modifications.val are read as u32 instead of u8 in FFmpeg.
Merged-by: Clément Bœsch <clement@stupeflix.com>

Fixes ./ffmpeg -skip_frame nokey -i h264/h264_intra_first-small.ts

Regression since c54e2740

* commit 'fa570590':
  h264: move initialising the implicit pred weight table for MBAFF
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '7b50d604':
  h264: call ff_h264_fill_mbaff_ref_list() when constructing the normal ref list
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit 'b16e9b9a':
  h264: move initialising the explicit pred weight table for MBAFF
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit 'b93c0aed':
  h264: drop an outdated comment

This commit is a noop, see 237d31e0Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '77a1e2c5':
  h264: move direct mode inits out of h264_slice_header_parse()
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit 'd06e4d8a':
  h264: start splitting decode_slice_header()
Merged-by: Clément Bœsch <clement@stupeflix.com>

This should not be needed anymore and simplifies the next merge
Requested-by: Clément Bœsch <u@pkh.me>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

This should not be needed anymore and simplifies the next merge
Requested-by: Clément Bœsch <u@pkh.me>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

Even though this is not part of the public API, some external
applications access fields after it, thus breaking after updating from
ffmpeg 3.0 or earlier.
Since it is not public, it can be freely moved to the end to avoid
that problem in the future.
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>

* commit '2940e196':
  vaapi_h265: cu_qp_delta should not be used in constant-QP mode
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '02fa1ad9':
  vaapi_h264: Add source version identifier as unregistered SEI
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '48e2967c':
  vaapi_h264: Add support for SEI messages
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '19d7667a':
  vaapi_encode: Add support for writing arbitrary additional packed headers
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '081961f8':
  vaapi_h264: Add support for VUI parameters
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '2e4a7bd5':
  h264: drop unused H264Context.gb
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '4f81f8db':
  Drop unnecessary golomb.h #includes
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '197ae68e':
  Drop unnecessary unary.h #includes
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '6ac52f05':
  dvbsub_parser: Add missing mem.h #include
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '81f769fa':
  gsm: Move requant_tab table to the gsm tables file
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '42dc2143':
  mpc: Drop unused GetBitContext context member
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '85b8403c':
  svq1enc: Drop unused GetBitContext context member
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '6d8fd614':
  vorbis: Kill some pointless debug code
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '59c6509d':
  mss2: Drop a silly assert
Merged-by: Clément Bœsch <clement@stupeflix.com>

This was mentioned to be in ae753dbd but
actually wasn't.

* commit 'b6686629':
  get_bits: Move BITSTREAM_READER_LE definition before all relevant #includes

The merge commit also includes changes for libavcodec/interplayacm.c and
libavcodec/truemotion2rt.c
Merged-by: Clément Bœsch <clement@stupeflix.com>

* commit '09c4e5c5':
  indeo2: Drop disabled big-endian ir2_codes table
Merged-by: Clément Bœsch <clement@stupeflix.com>