FreeBSD ipv6 multicast patch from ports tree

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@4507 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

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;