In rip6_input(), in case of multicast, we might skip the normal processing

and go to the next iteration early if multicast filtering would decide that
this socket shall not receive the data.
Unlock the pcb in that case or we leak the read lock and next time trying
to get a write lock, would hang forever.

PR:		kern/149608
Submitted by:	Chris Luke (chrisy flirble.org)
MFC after:	3 days

sys/netinet6/raw_ip6.c

@@ -248,6 +248,7 @@ rip6_input(struct mbuf **mp, int *offp, int proto)
 			}
 			if (blocked != MCAST_PASS) {
 				IP6STAT_INC(ip6s_notmember);
+				INP_RUNLOCK(in6p);
 				continue;
 			}
 		}