doxy header for udp protocol

Originally committed as revision 12861 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/udp.c

@@ -18,6 +18,12 @@
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
+
+/**
+ * @file udp.c
+ * UDP protocol
+ */
+
 #include "avformat.h"
 #include <unistd.h>
 #include "network.h"