net: reintroduce missing rcu_assign_pointer() calls

commit a9b3cd7f32 (rcu: convert uses of rcu_assign_pointer(x, NULL) to
RCU_INIT_POINTER) did a lot of incorrect changes, since it did a
complete conversion of rcu_assign_pointer(x, y) to RCU_INIT_POINTER(x,
y).

We miss needed barriers, even on x86, when y is not NULL.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Stephen Hemminger <shemminger@vyatta.com>
CC: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 0d38808..556b082 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -765,7 +765,7 @@
 	}
 
 	/* last thing to do is link it to the net device structure */
-	RCU_INIT_POINTER(ndev->npinfo, npinfo);
+	rcu_assign_pointer(ndev->npinfo, npinfo);
 
 	return 0;