macsec: add rcu_barrier() on module exit

Without this, the various uses of call_rcu could cause a kernel panic.

Fixes: c09440f7dc ("macsec: introduce IEEE 802.1AE driver")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/macsec.c

@@ -3361,6 +3361,7 @@ static void __exit macsec_exit(void)
 	genl_unregister_family(&macsec_fam);
 	rtnl_link_unregister(&macsec_link_ops);
 	unregister_netdevice_notifier(&macsec_notifier);
+	rcu_barrier();
 }
 
 module_init(macsec_init);