main/openrc: support rc_verbose variable in the networking service
From the default OpenRC configuration file:
# If you want verbose output for OpenRC, set this to yes. If you want # verbose output for service foo only, set it to yes in /etc/conf.d/foo. #rc_verbose=no
rc_verbose variable is also supported by other services, e.g.
/etc/init.d/local. The setting is activated by default to remain
backwards compatible but can be disabled if desired.