* Do not log events that are not critical (deadly) to the NIC router if not
configured to be verbose,
* Print almost all log lines with a prefix of the domain name they are
related to,
* And, do not use Genode::error and Genode::warning as they make it hard to
read the log with the domain name prefixes.
Fixes#2840
An IPv4 config (for a domain/interface of the router) consists of
an IPv4 address, a subnet prefix specifier, an optional gateway
IPv4 address, and some flags that declare whether these fields and
the config as a whole are valid. To make the handling of those
tightly connected values easier and less error prone, we encapsulate
them in a new class.
Ref #2534
