[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>

net/bridge/br_stp_bpdu.c

@@ -17,6 +17,7 @@
 #include <linux/netfilter_bridge.h>
 #include <linux/etherdevice.h>
 #include <linux/llc.h>
+#include <net/net_namespace.h>
 #include <net/llc.h>
 #include <net/llc_pdu.h>
 #include <asm/unaligned.h>
@@ -141,6 +142,9 @@ int br_stp_rcv(struct sk_buff *skb, struct net_device *dev,
 	struct net_bridge *br;
 	const unsigned char *buf;
 
+	if (dev->nd_net != &init_net)
+		goto err;
+
 	if (!p)
 		goto err;