The new NMSettingMacsec contains information necessary to establish a
MACsec connection. At the moment we support two different MACsec
modes, both using wpa_supplicant: PSK and EAP.
PSK mode is based on a static CAK key for the MACsec key agreement
protocol, while EAP mode derives keys from a 802.1x authentication and
thus requires the presence of a NMSetting8021x in the connection.
