wifi: iwlwifi: mvm: add fw link id allocation

Driver uses link_id as an index in the array. FW currently can
support only 2 concurrently active links per vif with the ids in the
range 0-3. Add a mapping of dirver link ids to fw link id and track the
number of active link ids.

Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230328104949.a53e5df49c33.I02b25648d2d5ca370c0697bf19d0d34724eae8a1@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>