Merge r182537 from head to stable/7:

In UDPv6, reduce scope of global udbinfo lock during append to last
  matching socket by dropping it before udp6_append(), and remove
  duplicate unlocks of udbinfo and inpcb in sysctl return path.

Approved by:	re (kensmith)

sys/netinet6/udp6_usrreq.c

@@ -307,9 +307,9 @@ udp6_input(struct mbuf **mp, int *offp, int proto)
 			goto badheadlocked;
 		}
 		INP_RLOCK(last);
+		INP_INFO_RUNLOCK(&udbinfo);
 		udp6_append(last, m, off, &fromsa);
 		INP_RUNLOCK(last);
-		INP_INFO_RUNLOCK(&udbinfo);
 		return (IPPROTO_DONE);
 	}
 	/*
@@ -464,8 +464,6 @@ udp6_getcred(SYSCTL_HANDLER_ARGS)
 		INP_INFO_RUNLOCK(&udbinfo);
 		error = ENOENT;
 	}
-	INP_RUNLOCK(inp);
-	INP_INFO_RUNLOCK(&udbinfo);
 	if (error == 0)
 		error = SYSCTL_OUT(req, &xuc, sizeof(struct xucred));
 	return (error);