netns: let net_generic take pointer-to-const args

This commit is same in nature as v2.6.37-rc1-755-g3654654f; the network
namespace itself is not modified when calling net_generic, so the
parameter can be const.
Signed-off-by: NJan Engelhardt <jengelh@medozas.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/netns/generic.h

@@ -30,7 +30,7 @@ struct net_generic {
 	void *ptr[0];
 };
 
-static inline void *net_generic(struct net *net, int id)
+static inline void *net_generic(const struct net *net, int id)
 {
 	struct net_generic *ng;
 	void *ptr;