Merge branch 'android-eap-tls'

Merge branch 'android-eap-tls'

This adds support for EAP-TLS authentication on Android.

EAP-only authentication is currently not allowed because the AAA identity
is not configurable, so to prevent anyone with a valid certificate from
impersonating the AAA server and thus the gateway, we authenticate the
gateway (like we do with other authentication methods).
Also, it's currently not possible to select a specific CA certificate to
authenticate the AAA server certificate, so it either must be issued by the
same CA as that of the gateway or automatic CA certificate selection must
be used.