wpa_supplicant: Add support for IPv6 with UDP ctrl_iface

wpa_supplicant: Add support for IPv6 with UDP ctrl_iface

Add IPv6 support when using udp/udp-remote control interface using the
following new build configuration options:

CONFIG_CTRL_IFACE=udp6
CONFIG_CTRL_IFACE=udp6-remote

This is useful for testing, while we don't need to assign IPv4 address
(static or using DHCP) and can just use auto configured IPv6 addresses
(link local, which is based on the MAC address). Also add scope id
support for link local case.

For example,
./wpa_cli
./wpa_cli -i ::1,9877
./wpa_cli -i fe80::203:7fff:fe05:69%wlan0,9877

Signed-off-by: Janusz Dziedzic <janusz.dziedzic@tieto.com>