[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/econet/af_econet.c b/net/econet/af_econet.c
index a2429db..7de3006 100644
--- a/net/econet/af_econet.c
+++ b/net/econet/af_econet.c
@@ -1065,6 +1065,9 @@
 	struct sock *sk;
 	struct ec_device *edev = dev->ec_ptr;
 
+	if (dev->nd_net != &init_net)
+		goto drop;
+
 	if (skb->pkt_type == PACKET_OTHERHOST)
 		goto drop;