Change net_conf_import() to only use libnet_conf API functions.

Change net_conf_import() to only use libnet_conf API functions.

More precisely, only import_process_service() is changed.
This removes all references to registry code from net_conf.c.

net_conf_import() is currently -- like net_conf_addshare() -- also
considered a high-level add-on, not an API function.

Michael
(This used to be commit b4dca117c09ddb9c8e7eea25c6cde3fbef8c692b)