Make the third octet of Country String configurable

Make the third octet of Country String configurable

The new hostapd.conf parameter country3 can now be used to configure the
third octet of the Country String that was previously hardcoded to ' '
(= 0x20).

For example:

All environments of the current frequency band and country (default)
country3=0x20

Outdoor environment only
country3=0x4f

Indoor environment only
country3=0x49

Noncountry entity (country_code=XX)
country3=0x58

IEEE 802.11 standard Annex E table indication: 0x01 .. 0x1f
Annex E, Table E-4 (Global operating classes)
country3=0x04

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>