[NETNS]: Process inet_confirm_addr in the correct namespace.

inet_confirm_addr can be called with NULL in_dev from arp_ignore iff
scope is RT_SCOPE_LINK.

Lets always pass the device and check for RT_SCOPE_LINK scope inside
inet_confirm_addr. This let us take network namespace from in_device a
need for an additional argument.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/arp.c

@@ -402,7 +402,6 @@ static int arp_ignore(struct in_device *in_dev, __be32 sip, __be32 tip)
 	case 3:	/* Do not reply for scope host addresses */
 		sip = 0;
 		scope = RT_SCOPE_LINK;
-		in_dev = NULL;
 		break;
 	case 4:	/* Reserved */
 	case 5: