sctp: support ipv6 nonlocal bind

This patch makes sctp support ipv6 nonlocal bind by adding
sp->inet.freebind and net->ipv6.sysctl.ip_nonlocal_bind
check in sctp_v6_available as what sctp did to support
ipv4 nonlocal bind (commit cdac4e0).

Reported-by: Shijoe George <spanjikk@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/ipv6.c

@@ -560,6 +560,7 @@ static int sctp_v6_is_any(const union sctp_addr *addr)
 static int sctp_v6_available(union sctp_addr *addr, struct sctp_sock *sp)
 {
 	int type;
+	struct net *net = sock_net(&sp->inet.sk);
 	const struct in6_addr *in6 = (const struct in6_addr *)&addr->v6.sin6_addr;
 
 	type = ipv6_addr_type(in6);
@@ -574,7 +575,8 @@ static int sctp_v6_available(union sctp_addr *addr, struct sctp_sock *sp)
 	if (!(type & IPV6_ADDR_UNICAST))
 		return 0;
 
-	return ipv6_chk_addr(sock_net(&sp->inet.sk), in6, NULL, 0);
+	return sp->inet.freebind || net->ipv6.sysctl.ip_nonlocal_bind ||
+		ipv6_chk_addr(net, in6, NULL, 0);
 }
 
 /* This function checks if the address is a valid address to be used for