net: netsec: enable tx-irq during open callback

Enable TX-irq as well during ndo_open() as we can not count upon
RX to arrive early enough to trigger the napi. This patch is critical
for installation over network.

Fixes: 533dd11a ("net: socionext: Add Synquacer NetSec driver")
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>