cnss2: Avoid idle restart completely if reboot is in progress

Check if reboot is in progress at the beginning of idle restart in
order to avoid it completely. Also check if reboot is in progress
after wait_for_completion since the event can be completed in the same
context of reboot notification and it needs to return failure for such
cases to caller to avoid other issues.

Change-Id: Iff250df5971ca4c9b885f52250547e2b45d89ac3
Signed-off-by: Yue Ma <yuem@codeaurora.org>