bonding: improve event debug usability

Seeing bonding debug log data along the lines of "event: 5" is a bit spartan,
and often requires a lookup table if you don't remember what every event is.
Make use of netdev_cmd_to_name for an improved debugging experience, so for
the prior example, you'll see: "bond_netdev_event received NETDEV_REGISTER"
instead (both are prefixed with the device for which the event pertains).

CC: Jay Vosburgh <j.vosburgh@gmail.com>
CC: Veaceslav Falico <vfalico@gmail.com>
CC: Andy Gospodarek <andy@greyhouse.net>
CC: netdev@vger.kernel.org
Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -3223,7 +3223,8 @@ static int bond_netdev_event(struct notifier_block *this,
 {
 	struct net_device *event_dev = netdev_notifier_info_to_dev(ptr);
 
-	netdev_dbg(event_dev, "event: %lx\n", event);
+	netdev_dbg(event_dev, "%s received %s\n",
+		   __func__, netdev_cmd_to_name(event));
 
 	if (!(event_dev->priv_flags & IFF_BONDING))
 		return NOTIFY_DONE;