bonding: Add function to get the xmit slave in active-backup mode

Add helper function to get the xmit slave in active-backup mode.
It's only one line function that return the curr_active_slave,
but it will used both in the xmit flow and by the new .ndo to get
the xmit slave.

Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

drivers/net/bonding/bond_main.c

@@ -4042,6 +4042,12 @@ static netdev_tx_t bond_xmit_roundrobin(struct sk_buff *skb,
 	return NETDEV_TX_OK;
 }
 
+static struct slave *bond_xmit_activebackup_slave_get(struct bonding *bond,
+						      struct sk_buff *skb)
+{
+	return rcu_dereference(bond->curr_active_slave);
+}
+
 /* In active-backup mode, we know that bond->curr_active_slave is always valid if
  * the bond has a usable interface.
  */
@@ -4051,7 +4057,7 @@ static netdev_tx_t bond_xmit_activebackup(struct sk_buff *skb,
 	struct bonding *bond = netdev_priv(bond_dev);
 	struct slave *slave;
 
-	slave = rcu_dereference(bond->curr_active_slave);
+	slave = bond_xmit_activebackup_slave_get(bond, skb);
 	if (slave)
 		bond_dev_queue_xmit(bond, skb, slave->dev);
 	else