[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/drivers/net/pppoe.c b/drivers/net/pppoe.c
index 53fcee2..60c0e4e 100644
--- a/drivers/net/pppoe.c
+++ b/drivers/net/pppoe.c
@@ -389,6 +389,9 @@
 	if (!(skb = skb_share_check(skb, GFP_ATOMIC)))
 		goto out;
 
+	if (dev->nd_net != &init_net)
+		goto drop;
+
 	if (!pskb_may_pull(skb, sizeof(struct pppoe_hdr)))
 		goto drop;
 
@@ -418,6 +421,9 @@
 	struct pppoe_hdr *ph;
 	struct pppox_sock *po;
 
+	if (dev->nd_net != &init_net)
+		goto abort;
+
 	if (!pskb_may_pull(skb, sizeof(struct pppoe_hdr)))
 		goto abort;