bonding:delete unused rlb_interval_counter

Now, alb_bond_info uses rx_ntt,rlb_update_delay_counter and
rlb_update_retry_counter to decide when to call rlb_update_rx_clients().

Signed-off-by: Weiping Pan(潘卫平) <panweiping3@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>