[IPV6]: Repair Incoming Interface Handling for Raw Socket.

Due to changes to enforce checking interface bindings,
sockets did not see loopback packets bound for our local address
on our interface.

e.g.)
  When we ping6 fe80::1%eth0, skb->dev points loopback_dev while
  IP6CB(skb)->iif indicates eth0.

This patch fixes the issue by using appropriate incoming interface,
in the sense of scoping architecture.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>