Add another known RTMP channel ID to enum.

From patch by Sergiy (mail = piratfm, gmail)

Originally committed as revision 20703 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/rtmppkt.h

@@ -34,6 +34,7 @@
 enum RTMPChannel {
     RTMP_NETWORK_CHANNEL = 2,   ///< channel for network-related messages (bandwidth report, ping, etc)
     RTMP_SYSTEM_CHANNEL,        ///< channel for sending server control messages
+    RTMP_SOURCE_CHANNEL,        ///< channel for sending a/v to server
     RTMP_VIDEO_CHANNEL = 8,     ///< channel for video data
     RTMP_AUDIO_CHANNEL,         ///< channel for audio data
 };