Copy IPv4 multicast TTL from RTP to RTCP.

We were sending RTCP with TTL=1 all the time...
(cherry picked from commit 7da51390)

modules/stream_out/rtcp.c

@@ -99,6 +99,16 @@ rtcp_sender_t *OpenRTCP (vlc_object_t *obj, int rtp_fd, int proto,
         dport++;
 
         fd = net_OpenDgram (obj, src, sport, dst, dport, AF_UNSPEC, proto);
+
+        /* Copy the multicast IPv4 TTL value (useless for IPv6) */
+        if (fd != -1)
+        {
+            int ttl;
+            socklen_t len = sizeof (ttl);
+
+            if (!getsockopt (rtp_fd, SOL_IP, IP_MULTICAST_TTL, &ttl, &len))
+                setsockopt (fd, SOL_IP, IP_MULTICAST_TTL, &ttl, len);
+        }
     }
 
     if (fd == -1)