rcu: convert uses of rcu_assign_pointer(x, NULL) to RCU_INIT_POINTER

When assigning a NULL value to an RCU protected pointer, no barrier
is needed. The rcu_assign_pointer, used to handle that but will soon
change to not handle the special case.

Convert all rcu_assign_pointer of NULL value.

//smpl
@@ expression P; @@

- rcu_assign_pointer(P, NULL)
+ RCU_INIT_POINTER(P, NULL)

// </smpl>

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/8021q/vlan.c

@@ -133,7 +133,7 @@ void unregister_vlan_dev(struct net_device *dev, struct list_head *head)
 	if (grp->nr_vlans == 0) {
 		vlan_gvrp_uninit_applicant(real_dev);
 
-		rcu_assign_pointer(real_dev->vlgrp, NULL);
+		RCU_INIT_POINTER(real_dev->vlgrp, NULL);
 
 		/* Free the group, after all cpu's are done. */
 		call_rcu(&grp->rcu, vlan_rcu_free);