wifi: iwlwifi: mvm: refactor iwl_mvm_sta

As the new MLD API is introduced, we have a new enumeration
for the different station types. Since struct iwl_mvm_sta's
sta_type field will be in use for both new and old API,
change its type to a unified one, so it can hold both.

Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230320122330.c8b86d8ddd3e.I9581235860b91654b4f6c3a8797c777702690998@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>