sctp: avoid compiler warning on implicit fallthru

These fall-through are expected.

Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Reviewed-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/ipv6.c

@@ -826,6 +826,7 @@ static int sctp_inet6_af_supported(sa_family_t family, struct sctp_sock *sp)
 	case AF_INET:
 		if (!__ipv6_only_sock(sctp_opt2sk(sp)))
 			return 1;
+		/* fallthru */
 	default:
 		return 0;
 	}