nl80211: add PROTECTED_TWT nl80211 extended feature

Add API for telling whether the driver supports protected TWT.
The protected_twt capability in the RSNXE will be based on this.

Signed-off-by: Shaul Triebitz <shaul.triebitz@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/20200131111300.891737-23-luca@coelho.fi


Signed-off-by: Johannes Berg <johannes.berg@intel.com>