[NET]: Make packet reception network namespace safe

This patch modifies every packet receive function
registered with dev_add_pack() to drop packets if they
are not from the initial network namespace.

This should ensure that the various network stacks do
not receive packets in a anything but the initial network
namespace until the code has been converted and is ready
for them.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ax25/ax25_in.c b/net/ax25/ax25_in.c
index 0ddaff0..3b7d172 100644
--- a/net/ax25/ax25_in.c
+++ b/net/ax25/ax25_in.c
@@ -451,6 +451,11 @@
 	skb->sk = NULL;		/* Initially we don't know who it's for */
 	skb->destructor = NULL;	/* Who initializes this, dammit?! */
 
+	if (dev->nd_net != &init_net) {
+		kfree_skb(skb);
+		return 0;
+	}
+
 	if ((*skb->data & 0x0F) != 0) {
 		kfree_skb(skb);	/* Not a KISS data frame */
 		return 0;