netfilter: netns nf_conntrack: pass netns pointer to nf_conntrack_in()

It's deducible from skb->dev or skb->dst->dev, but we know netns at
the moment of call, so pass it down and use for finding and creating
conntracks.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

include/net/netfilter/nf_conntrack_core.h

@@ -20,7 +20,8 @@
 /* This header is used to share core functionality between the
    standalone connection tracking module, and the compatibility layer's use
    of connection tracking. */
-extern unsigned int nf_conntrack_in(u_int8_t pf,
+extern unsigned int nf_conntrack_in(struct net *net,
+				    u_int8_t pf,
 				    unsigned int hooknum,
 				    struct sk_buff *skb);