iwlwifi: mvm: reserve sta_id 0 to station

The d3/d0i3 fw code requires the sta_id to be 0
(this is used to determine the rates and keys
to use in arp offloading).

Reserve sta_id 0 to station interface in order
to comply with this requirement.

Change some functions prototypes in order to
make the allocation function know about
the interface type.

Signed-off-by: Eliad Peller <eliadx.peller@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>