FreeBSD ipv6 multicast patch from ports tree

Originally committed as revision 4507 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/udp.c

@@ -28,6 +28,11 @@
 #endif
 #include <netdb.h>
 
+#ifndef IPV6_ADD_MEMBERSHIP
+#define IPV6_ADD_MEMBERSHIP IPV6_JOIN_GROUP
+#define IPV6_DROP_MEMBERSHIP IPV6_LEAVE_GROUP
+#endif
+
 typedef struct {
     int udp_fd;
     int ttl;