Fix the lavf docs, we have a RTP muxer, not a demuxer

Originally committed as revision 24548 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/general.texi

@@ -212,7 +212,7 @@ library:
 @item Lego Mindstorms RSO       @tab X @tab X
 @item RTMP                      @tab X @tab X
     @tab Output is performed by publishing stream to RTMP server
-@item RTP                       @tab   @tab X
+@item RTP                       @tab X @tab
 @item RTSP                      @tab X @tab X
 @item SDP                       @tab   @tab X
 @item Sega FILM/CPK             @tab   @tab X