dbus-broker.service has a 'dbus.service' alias which is installed when the
service gets enabled.
If the alias is not present in the initrd image, services requiring D-Bus in
the initrd fail to start because they depend on dbus.service, which doesn't
exist.
Therefore, enable the service to create the alias.
This rephrases a comment in the check() as requested on another PR
and generalizes the install() section comments on par with other recent
module changes.
Harald Hoyer