Core Network and ENB use dnsmasq for completely different purposes:

- core network uses it to provide DNS server, while
- enb uses dnsmasq to provide DHCP server for Radio Units to be able to access
  Control & Management channel on the CPRI link.

-> Even though both those services are handled via same dnsmasq program, it
   makes sense to split dnsmasq config for clarity and as preparation for
   further adjustments of enb part.

   We also push config rendering down to -core and -enb instances also for
   clarity, and because in enb case rendering will need to know set of
   configured Radio Units - information that will become loaded only at
   instance-enb.

/cc @jhuge, @xavier_thompson, @Daetalus
/reviewed-by @lu.xu
/reviewed-on nexedi/slapos!1472