net: stmmac: use netif_tx_start|stop_all_queues() function

The current implementation of stmmac_stop_all_queues() and
stmmac_start_all_queues() will not work correctly when the value of
tx_queues_to_use is changed through ethtool -L DEVNAME rx N tx M command.

Also, netif_tx_start|stop_all_queues() are only needed in driver open()
and close() only.

Fixes: c22a3f48 net: stmmac: adding multiple napi mechanism

Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: Voon Weifeng <weifeng.voon@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>