iwlwifi: mvm: fix ht protection flags

The HT protection flags have been a mess for a long time,
this patch fixes all this.

The proper source of information for this is the
protection in the HT operation mode IE which is
propagated to bss_conf by mac80211.

1) No need to set the HT protection flags when the link
   doesn't support HT.
2) We need to set the TGG protection when ERP is active.

Signed-off-by: Avri Altman <avri.altman@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>