iwlwifi: mvm: update offloaded rate control on changes

With offloaded rate control, if the station parameters (rates, NSS,
bandwidth) change (sta_rc_update method), call iwl_mvm_rs_rate_init()
to propagate those change to the firmware.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>