dbus: Reload if /etc/dbus-1 changes

Specifically, this fixes dnsmasq, which failed with

  Apr 16 19:00:30 mandark dnsmasq[23819]: dnsmasq: DBus error: Connection ":1.260" is not allowed to own the service "uk.org.thekelleys.dnsmasq" due to security policies in the configuration file
  Apr 16 19:00:30 mandark dnsmasq[23819]: DBus error: Connection ":1.260" is not allowed to own the service "uk.org.thekelleys.dnsmasq" due to security policies in the configuration file

after being enabled, due to dbus not being reloaded.