iwlwifi: mvm: always init rs with 20mhz bandwidth rates

In AP mode, when a new station associates, rs is initialized immediately
upon association completion, before the phy context is updated with the
association parameters, so the sta bandwidth might be wider than the phy
context allows.
To avoid this issue, always initialize rs with 20mhz bandwidth rate, and
after authorization, when the phy context is already up-to-date, re-init
rs with the correct bw.

Signed-off-by: Naftali Goldstein <naftali.goldstein@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>