sctp: Fix ECN markings for IPv6

Commit e9df2e8fd8fbc95c57dbd1d33dada66c4627b44c ("[IPV6]: Use
appropriate sock tclass setting for routing lookup.") also changed the
way that ECN capable transports mark this capability in IPv6.  As a
result, SCTP was not marking ECN capablity because the traffic class
was never set.  This patch brings back the markings for IPv6 traffic.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 714dc43..7f25195 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -588,6 +588,7 @@
 	int		(*is_ce)	(const struct sk_buff *sk);
 	void		(*seq_dump_addr)(struct seq_file *seq,
 					 union sctp_addr *addr);
+	void		(*ecn_capable)(struct sock *sk);
 	__u16		net_header_len;
 	int		sockaddr_len;
 	sa_family_t	sa_family;