software/ors-amarisoft: Activate for-RU DHCP server automatically

instead of requiring users to explicitly activate it via additional `dnsmasq` parameter.

The reason here is simple: CPRI-based radio units, for example Lopcomm ORAN RU,
need to be configured to go to radio, and for that configuration to work we
need to be able to talk via TCP/IP to the RU.

/cc @jhuge, @xavier_thompson, @Daetalus
/reviewed-by @lu.xu
/reviewed-on nexedi/slapos!1479