net: original ingress device index in PKTINFO

Applications such as OSPF and BFD need the original ingress device not
the VRF device; the latter can be derived from the former. To that end
add the skb_iif to inet_skb_parm and set it in ipv4 code after clearing
the skb control buffer similar to IPv6. From there the pktinfo can just
pull it from cb with the PKTINFO_SKB_CB cast.

The previous patch moving the skb->dev change to L3 means nothing else
is needed for IPv6; it just works.

Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip.h

@@ -36,6 +36,7 @@
 struct sock;
 
 struct inet_skb_parm {
+	int			iif;
 	struct ip_options	opt;		/* Compiled IP options		*/
 	unsigned char		flags;