iwlwifi: mvm: make sure internal station has a valid id

If the driver failed to resume from D3, it is possible that it has
no valid aux station. In such case, fw restart will end up in sending
station related commands with an invalid station id, which will
result in an assert.

Fix this by allocating a new station id for the aux station if it
does not have a valid id even in the case of fw restart.

Signed-off-by: Avraham Stern <avraham.stern@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>