netfilter: Pass net into okfn

This is immediately motivated by the bridge code that chains functions that
call into netfilter.  Without passing net into the okfns the bridge code would
need to guess about the best expression for the network namespace to process
packets in.

As net is frequently one of the first things computed in continuation functions
after netfilter has done it's job passing in the desired network namespace is in
many cases a code simplification.

To support this change the function dst_output_okfn is introduced to
simplify passing dst_output as an okfn.  For the moment dst_output_okfn
just silently drops the struct net.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/dev.c b/net/core/dev.c
index 7db9b01..00dccfa 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2915,9 +2915,11 @@
 
 /**
  *	dev_loopback_xmit - loop back @skb
+ *	@net: network namespace this loopback is happening in
+ *	@sk:  sk needed to be a netfilter okfn
  *	@skb: buffer to transmit
  */
-int dev_loopback_xmit(struct sock *sk, struct sk_buff *skb)
+int dev_loopback_xmit(struct net *net, struct sock *sk, struct sk_buff *skb)
 {
 	skb_reset_mac_header(skb);
 	__skb_pull(skb, skb_network_offset(skb));