libertas: support USB persistence on suspend/resume (resend)

Handle .reset_resume() so that libertas can survive suspend/resume without
reloading the firmware.

Signed-off-by: Andrey Yurovsky <andrey@cozybit.com>
Acked-by: Deepak Saxena <dsaxena@laptop.org>
Acked-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>