cnss2: Fix synchronization issues related to idle shutdown

If system suspend/resume is going on, reject idle shutdown request
so that WLAN driver can restart the timer. Also there is a chance
that while idle shutdown is in progress, user requests interface up
for WLAN driver. Handle this case by checking the return code from
idle shutdown callback.

Change-Id: If41bf43ed974d1759ed336a012c1af1182f00268
Signed-off-by: Yue Ma <yuem@codeaurora.org>