[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/ipv6/ip6_input.c b/net/ipv6/ip6_input.c
index 30a5cb1..7d18cac 100644
--- a/net/ipv6/ip6_input.c
+++ b/net/ipv6/ip6_input.c
@@ -61,6 +61,11 @@
 	u32 		pkt_len;
 	struct inet6_dev *idev;
 
+	if (dev->nd_net != &init_net) {
+		kfree_skb(skb);
+		return 0;
+	}
+
 	if (skb->pkt_type == PACKET_OTHERHOST) {
 		kfree_skb(skb);
 		return 0;