netns xfrm: lookup in netns

Pass netns to xfrm_lookup()/__xfrm_lookup(). For that pass netns
to flow_cache_lookup() and resolver callback.

Take it from socket or netdevice. Stub DECnet to init_net.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 4e6959c..77bfba9 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2761,7 +2761,7 @@
 			flp->fl4_src = (*rp)->rt_src;
 		if (!flp->fl4_dst)
 			flp->fl4_dst = (*rp)->rt_dst;
-		err = __xfrm_lookup((struct dst_entry **)rp, flp, sk,
+		err = __xfrm_lookup(net, (struct dst_entry **)rp, flp, sk,
 				    flags ? XFRM_LOOKUP_WAIT : 0);
 		if (err == -EREMOTE)
 			err = ipv4_dst_blackhole(net, rp, flp);