We observed that packets and bytes count are not reset
when user performs interface down. Eventually, tx queue is
exhausted and packets will not be sent out.
To avoid this problem, resets tx queue in ndo_stop.

Fixes: 533dd11a ("net: socionext: Add Synquacer NetSec driver")
Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Signed-off-by: Yoshitoyo Osaki <osaki.yoshitoyo@socionext.com>
Signed-off-by: David S. Miller <davem@davemloft.net>