xfrm: Fix warning in xfrm6_tunnel_net_exit.

We need to make sure that all states are really deleted
before we check that the state lists are empty. Otherwise
we trigger a warning.

Fixes: baeb0dbbb5659 ("xfrm6_tunnel: exit_net cleanup check added")
Reported-and-tested-by:[e-mail]
Signed-off-by: Steffen Klassert <[e-mail]>

include/net/xfrm.h

···
 int xfrm_input_register_afinfo(const struct xfrm_input_afinfo *afinfo);
 int xfrm_input_unregister_afinfo(const struct xfrm_input_afinfo *afinfo);
 
+void xfrm_flush_gc(void);
 void xfrm_state_delete_tunnel(struct xfrm_state *x);
 
 struct xfrm_type {

net/ipv6/xfrm6_tunnel.c

···
 	struct xfrm6_tunnel_net *xfrm6_tn = xfrm6_tunnel_pernet(net);
 	unsigned int i;
 
+	xfrm_state_flush(net, IPSEC_PROTO_ANY, false);
+	xfrm_flush_gc();
+
 	for (i = 0; i < XFRM6_TUNNEL_SPI_BYADDR_HSIZE; i++)
 		WARN_ON_ONCE(!hlist_empty(&xfrm6_tn->spi_byaddr[i]));
 

net/xfrm/xfrm_state.c

···
 	return afinfo;
 }
 
+void xfrm_flush_gc(void)
+{
+	flush_work(&xfrm_state_gc_work);
+}
+EXPORT_SYMBOL(xfrm_flush_gc);
+
 /* Temporarily located here until net/xfrm/xfrm_tunnel.c is created */
 void xfrm_state_delete_tunnel(struct xfrm_state *x)
 {