r8152: avoid start_xmit to call napi_schedule during autosuspend

Adjust the setting of the flag of SELECTIVE_SUSPEND to prevent start_xmit()
from calling napi_schedule() directly during runtime suspend.

After calling napi_disable() or clearing the flag of WORK_ENABLE,
scheduling the napi is useless.

Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>