net: socket: Start socket service earlier

Make sure that socket service is started earlier than
config library. This is enforced in config libs init.c
but set the default value here too.
The reason for this is that the config library might need
to start dhcpv4 server which needs socket service to work,
so the ordering is important here.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>