mwifiex: skipping pending commands after unload

We skip downloading other commands after FUNC_SHUTDOWN is queued
during driver unload. Main thread should be woken up each time
after freeing skipped command so that FUNC_SHUTDOWN gets served
in case if there are other pending commands before FUNC_SHUTDOWN.
Also, call mwifiex_complete_cmd() only for synchronous commands.

Reported-by: Avery Pennarun <apenwarr@gmail.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Maithili Hinge <maithili@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>