sctp: add skb_sdif in struct sctp_af

Add skb_sdif function in struct sctp_af to get the enslaved device
for both ipv4 and ipv6 when adding SCTP VRF support in sctp_rcv in
the next patch.
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sctp/structs.h

@@ -477,6 +477,7 @@ struct sctp_af {
 	int		(*available)	(union sctp_addr *,
 					 struct sctp_sock *);
 	int		(*skb_iif)	(const struct sk_buff *sk);
+	int		(*skb_sdif)(const struct sk_buff *sk);
 	int		(*is_ce)	(const struct sk_buff *sk);
 	void		(*seq_dump_addr)(struct seq_file *seq,
 					 union sctp_addr *addr);

net/sctp/ipv6.c

@@ -842,7 +842,12 @@ static int sctp_v6_addr_to_user(struct sctp_sock *sp, union sctp_addr *addr)
 /* Where did this skb come from?  */
 static int sctp_v6_skb_iif(const struct sk_buff *skb)
 {
-	return IP6CB(skb)->iif;
+	return inet6_iif(skb);
+}
+
+static int sctp_v6_skb_sdif(const struct sk_buff *skb)
+{
+	return inet6_sdif(skb);
 }
 
 /* Was this packet marked by Explicit Congestion Notification? */
@@ -1142,6 +1147,7 @@ static struct sctp_af sctp_af_inet6 = {
 	.is_any		   = sctp_v6_is_any,
 	.available	   = sctp_v6_available,
 	.skb_iif	   = sctp_v6_skb_iif,
+	.skb_sdif	   = sctp_v6_skb_sdif,
 	.is_ce		   = sctp_v6_is_ce,
 	.seq_dump_addr	   = sctp_v6_seq_dump_addr,
 	.ecn_capable	   = sctp_v6_ecn_capable,

net/sctp/protocol.c

@@ -567,6 +567,11 @@ static int sctp_v4_skb_iif(const struct sk_buff *skb)
 	return inet_iif(skb);
 }
 
+static int sctp_v4_skb_sdif(const struct sk_buff *skb)
+{
+	return inet_sdif(skb);
+}
+
 /* Was this packet marked by Explicit Congestion Notification? */
 static int sctp_v4_is_ce(const struct sk_buff *skb)
 {
@@ -1185,6 +1190,7 @@ static struct sctp_af sctp_af_inet = {
 	.available	   = sctp_v4_available,
 	.scope		   = sctp_v4_scope,
 	.skb_iif	   = sctp_v4_skb_iif,
+	.skb_sdif	   = sctp_v4_skb_sdif,
 	.is_ce		   = sctp_v4_is_ce,
 	.seq_dump_addr	   = sctp_v4_seq_dump_addr,
 	.ecn_capable	   = sctp_v4_ecn_capable,