rtpdec: Allow dynamic payload handlers to handle static payload types, too

Originally committed as revision 25890 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/rtpdec.h

@@ -116,6 +116,9 @@ struct RTPDynamicProtocolHandler_s {
     const char enc_name[50];    /* XXX: still why 50 ? ;-) */
     enum AVMediaType codec_type;
     enum CodecID codec_id;
+    int static_payload_id; /* 0 means no payload id is set. 0 is a valid
+                            * payload ID (PCMU), too, but that format doesn't
+                            * require any custom depacketization code. */
 
     // may be null
     int (*parse_sdp_a_line) (AVFormatContext *s,