hostapd: add interworking support

hostapd: add interworking support

This adds configuration options to enable interworking for hostapd.
All options require iw_enabled to be set to 1 for a given VAP.

All IEEE802.11u related settings are supported with exception of the
venue information which will be added as separate UCI sections at a
later point.

The options use the same name as the ones from the hostapd.conf file
with a "iw_" prefix added.

All UCI configuration options are passed without further modifications
to hostapd with exceptions of the following options, whose elements can
be provided using UCI lis elements:

 - iw_roaming_consortium
 - iw_anqp_elem
 - iw_nai_realm
 - iw_domain_name
 - iw_anqp_3gpp_cell_net

Signed-off-by: David Bauer <mail@david-bauer.net>