NFSD: Clean up _lm_ operation names

The common practice is to name function instances the same as the
method names, but with a uniquifying prefix. Commit aef9583b


("NFSD: Get reference of lockowner when coping file_lock") missed
this -- the new function names should both have been of the form
"nfsd4_lm_*".

Before more lock manager operations are added in NFSD, rename these
two functions for consistency.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>