check-gateway: stop dhcp server if batman gateway modus is off
maintenance: Deactivate radvd and dhcpd really.

When in maintenance it is usual to restart the machine, e.g. after an
kernel update, so we don't want radvd to be started when we are still
in maintenance.
Merge pull request #64 from sargon/dhcp-deactivate

This looks fine to me. I will close the issue #49 after merging this.