configure: Fix standalone compilation of the rtp muxer.

Reported and suggested by: me at juneoh dot net

Fixes ticket #5989.

configure

@@ -2908,6 +2908,7 @@ ogv_muxer_select="ogg_muxer"
 opus_muxer_select="ogg_muxer"
 psp_muxer_select="mov_muxer"
 rtp_demuxer_select="sdp_demuxer"
+rtp_muxer_select="golomb"
 rtpdec_select="asf_demuxer jpegtables mov_demuxer mpegts_demuxer rm_demuxer rtp_protocol srtp"
 rtsp_demuxer_select="http_protocol rtpdec"
 rtsp_muxer_select="rtp_muxer http_protocol rtp_protocol rtpenc_chain"