NLM: Remove "create" argument from nsm_find()

Clean up: nsm_find() now has only one caller, and that caller
unconditionally sets the @create argument. Thus the @create
argument is no longer needed.

Since nsm_find() now has a more specific purpose, pick a more
appropriate name for it.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>