bonding: do not set slave_dev npinfo before slave_enable_netpoll in bond_enslave

After Commit 8a8efa22 ("bonding: sync netpoll code with bridge"), it
would set slave_dev npinfo in slave_enable_netpoll when enslaving a dev
if bond->dev->npinfo was set.

However now slave_dev npinfo is set with bond->dev->npinfo before calling
slave_enable_netpoll. With slave_dev npinfo set, __netpoll_setup called
in slave_enable_netpoll will not call slave dev's .ndo_netpoll_setup().
It causes that the lower dev of this slave dev can't set its npinfo.

One way to reproduce it:

  # modprobe bonding
  # brctl addbr br0
  # brctl addif br0 eth1
  # ifconfig bond0 192.168.122.1/24 up
  # ifenslave bond0 eth2
  # systemctl restart netconsole
  # ifenslave bond0 br0
  # ifconfig eth2 down
  # systemctl restart netconsole

The netpoll won't really work.

This patch is to remove that slave_dev npinfo setting in bond_enslave().

Fixes: 8a8efa22 ("bonding: sync netpoll code with bridge")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -1660,8 +1660,7 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev,
 	} /* switch(bond_mode) */
 
 #ifdef CONFIG_NET_POLL_CONTROLLER
-	slave_dev->npinfo = bond->dev->npinfo;
-	if (slave_dev->npinfo) {
+	if (bond->dev->npinfo) {
 		if (slave_enable_netpoll(new_slave)) {
 			netdev_info(bond_dev, "master_dev is using netpoll, but new slave device does not support netpoll\n");
 			res = -EBUSY;