[XFRM]: Purge dst references to deleted SAs passively.

Just let GC and other normal mechanisms take care of getting
rid of DST cache references to deleted xfrm_state objects
instead of walking all the policy bundles.

Signed-off-by: David S. Miller <davem@davemloft.net>

net/xfrm/xfrm_policy.c

@@ -1472,7 +1472,7 @@ static void __xfrm_garbage_collect(void)
 	xfrm_prune_bundles(unused_bundle);
 }
 
-int xfrm_flush_bundles(void)
+static int xfrm_flush_bundles(void)
 {
 	xfrm_prune_bundles(stale_bundle);
 	return 0;