Set the STA_FLG_RTS_MIMO_PROT bit in station_flags_msk of the add sta
command, so that when smps mode changes, the FW will know about it.

In particular, in AP mode, clients are added upon receival of an auth
request, at which point there's no knowledge of the client's smps mode.
When the assoc request arrives, the add_sta command is resent to modify
the station parameters. At this point the driver knows the smps mode,
but since the corresponding bit in the mask is not set, the fw doesn't
update this field so there's no rts protection for mimo.

Fixes: 5bc5aaad ("iwlwifi: mvm: set up initial SMPS/NSS station info")
Signed-off-by: Naftali Goldstein <naftali.goldstein@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>