login: allow non-console sessions to change vt

When starting a wayland session through a systemd service for a non-root
user, the compositor (based on wlroots) is denied the authorization to
change vt.
Once the user logs in, either through a local console or via ssh, the
compositor can work properly.

This is related to the login polkit policy:
- `allow_inactive` has value `auth_admin_keep`, denying any non-root
  user session the authorization to change vt
- `allow_active` has value `yes`, which explains why the vt change
  becomes possible once the user logs in through another channel

By changing the `allow_inactive` value to `yes`, any user session setup
in a service file can switch vt, allowing wayland sessions for non-root
users.

(cherry picked from commit 19bb87fb)