nfsd: convert to using new filelock helpers

Convert to using the new file locking helper functions. Also, in later
patches we're going to introduce some macros with names that clash with
the variable names in nfsd4_lock. Rename them.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/20240131-flsplit-v3-12-c6129007ee8d@kernel.org


Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>