nfsd: make local functions static

This also fixes a number of sparse warnings.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: J. Bruce Fields <bfields@fieldses.org>
Cc: Neil Brown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>