garp: remove one synchronize_rcu() call

Speedup vlan dismantling in CONFIG_VLAN_8021Q_GVRP=y cases,
by using a call_rcu() to free the memory instead of waiting with
expensive synchronize_rcu() [ while RTNL is held ]

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Ben Greear <greearb@candelatech.com>
Cc: Patrick McHardy <kaber@trash.net>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/garp.h b/include/net/garp.h
index f4c2959..8cabbf08 100644
--- a/include/net/garp.h
+++ b/include/net/garp.h
@@ -108,6 +108,7 @@
 
 struct garp_port {
 	struct garp_applicant __rcu	*applicants[GARP_APPLICATION_MAX + 1];
+	struct rcu_head			rcu;
 };
 
 extern int	garp_register_application(struct garp_application *app);