lockd: prepare nlm_lockowner for use by the server

The nlm_lockowner structure that the client uses to track locks is
generally useful to the server as well.  Very similar functions to handle
allocation and tracking of the nlm_lockowner will follow. Rename the client
functions for clarity.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>