We cannot always start the service monitor thread statically
because the static threads are started after the application
level. This means that when config library wants to start
dhcpv4 server which uses socket services, there would be a
deadlock. Simplest solution is to start the service thread
directly from socket service init function.
Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>