iwlwifi: mvm: support ADD_STA_CMD_API_S ver 12

ADD_STA_CMD_API_S ver 12 was added in order to properly support
auxiliary activities in CDB NICs. In the new version we don't need
to allocate an aux station at initialization, instead we add an
aux station only when an auxiliary activity that requires a dedicated Tx
queue is needed. For now the only case we need this kind of activity is
when using hot spot 2.0

Signed-off-by: Nathan Errera <nathan.errera@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/iwlwifi.20201008180656.700e6e2e3077.Icdd807b6a3ad3fed806449ea0a13f856aa20e632@changeid