netns xfrm: per-netns state GC list

km_waitq is going to be made per-netns to disallow spurious wakeups
in __xfrm_lookup().

To not wakeup after every garbage-collected xfrm_state (which potentially
can be from different netns) make state GC list per-netns.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/netns/xfrm.h b/include/net/netns/xfrm.h
index bd68802..8ceb765 100644
--- a/include/net/netns/xfrm.h
+++ b/include/net/netns/xfrm.h
@@ -20,6 +20,7 @@
 	unsigned int		state_hmask;
 	unsigned int		state_num;
 	struct work_struct	state_hash_work;
+	struct hlist_head	state_gc_list;
 };
 
 #endif