icnss: block modem shutdown during driver reinit

Sending modem shutdown request during WLAN driver re-init
sequence will lead to the situation that WLAN FW will not
responding as modem/WLAN PD is down. Hence block modem
shutdown request when WLAN driver is doing re-init.

Change-Id: I8eae4daf5883925b6f7ee2ac14851bdcec285c94
CRs-Fixed: 2391616
Signed-off-by: Yuanyuan Liu <yuanliu@codeaurora.org>