avformat/udp: fix build on MINIX

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/udp.c

@@ -647,7 +647,9 @@ static int udp_open(URLContext *h, const char *uri, int flags)
     }
 
     if (s->is_broadcast) {
+#ifdef SO_BROADCAST
         if (setsockopt (udp_fd, SOL_SOCKET, SO_BROADCAST, &(s->is_broadcast), sizeof(s->is_broadcast)) != 0)
+#endif
            goto fail;
     }