[NETNS][IPV6] udp - make proc handle the network namespace

This patch makes the common udp proc functions to take care of which
socket they should show taking into account the namespace it belongs.

Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/udp.h

@@ -192,6 +192,7 @@ struct udp_seq_afinfo {
 };
 
 struct udp_iter_state {
+	struct net              *net;
 	sa_family_t		family;
 	struct hlist_head	*hashtable;
 	int			bucket;