init: specify we do IPv4 for now

This to ensure an interface with IPv6 address will be seen as
configured.
init: indent
doc: libfrontier-rpc-perl is a new debian dep

Perl Frontier::Client lib was introduced as a new dependency by
6b99356a4a2702ad34fd94d87bc8354b2748f706

On Debian, the package is called libfrontier-rpc-perl