hostapd: Configure spectrum management capability

hostapd: Configure spectrum management capability

Add configuration of Spectrum Management subfield in the Capability
Information of Beacon, Probe Response, and Association Response frames.
Spectrum Management bit is set when directly requested by new
configuration option spectrum_mgmt_required=1 or when AP is running on
DFS channels. In the future, also TPC shall require this bit to be set.

Signed-hostap: Srinivasan <srinivasanb@posedge.com>
Signed-hostap: Chaitanya T K <chaitanyatk@posedge.com>
Signed-hostap: Marek Puzyniak <marek.puzyniak@tieto.com>