netcfg-copy-config: exit if connection type file is missing

finish-install.d/55netcfg-copy-config: Exit if connection type
information was not written by netcfg. This preserves the generated
/etc/network/interfaces on kFreeBSD. It will also preserved files
generated by users between base install and finishing. (Closes: #698626)

Signed-off-by: Philipp Kern <pkern@debian.org>
releasing version 1.106
non-native package