Allow hostapd config file for dynamically added interface

Allow hostapd config file for dynamically added interface

This extends hostapd global control interface command "ADD" to use a
configuration file instead of requiring configuration to be built using
SET command.

The command format is now following:
ADD <ifname> <control path|config=<path to config>>

For example:

ADD wlan0 /var/run/hostapd
ADD wlan0 config=/tmp/hostapd.conf

When using the configuration file option, ctrl_interface parameter in
the file needs to be set to allow ENABLE command to be issued on the new
interface.

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