sctp: add support for setting flowlabel when adding a transport

Struct sockaddr_in6 has the member sin6_flowinfo that includes the
ipv6 flowlabel, it should also support for setting flowlabel when
adding a transport whose ipaddr is from userspace.

Note that addrinfo in sctp_sendmsg is using struct in6_addr for
the secondary addrs, which doesn't contain sin6_flowinfo, and
it needs to copy sin6_flowinfo from the primary addr.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sctp/associola.c b/net/sctp/associola.c
index 16ecfbc..297d9cf 100644
--- a/net/sctp/associola.c
+++ b/net/sctp/associola.c
@@ -650,8 +650,16 @@ struct sctp_transport *sctp_assoc_add_peer(struct sctp_association *asoc,
 	peer->sackdelay = asoc->sackdelay;
 	peer->sackfreq = asoc->sackfreq;
 
-	if (addr->sa.sa_family == AF_INET6)
-		peer->flowlabel = asoc->flowlabel;
+	if (addr->sa.sa_family == AF_INET6) {
+		__be32 info = addr->v6.sin6_flowinfo;
+
+		if (info) {
+			peer->flowlabel = ntohl(info & IPV6_FLOWLABEL_MASK);
+			peer->flowlabel |= SCTP_FLOWLABEL_SET_MASK;
+		} else {
+			peer->flowlabel = asoc->flowlabel;
+		}
+	}
 	peer->dscp = asoc->dscp;
 
 	/* Enable/disable heartbeat, SACK delay, and path MTU discovery