iwlwifi: dump debug data before stop device

Debug data dump is not working in flows that stop the device is used
in their error handling. During these flows the op mode mutex is
locked until the device stops.  Because of that, any assert generated
from the firmware can be handled only after the device already
stopped.

Since dumping cannot occour after stopping the device, split the the
dump function to two parts, Part that handles locking, and the part
that starts the actual dumping and call the second part in the op mode
stop device function.

Signed-off-by: Shahar S Matityahu <shahar.s.matityahu@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>