hostapd: rework .config and bump to version 2.1

Rework .config file editing as was done for wpa_supplicant and bump to
version 2.1 which includes 802.11ac and ACS support.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>