lockd: Move nlmdbg_cookie2a() to svclock.c

Clean up.  nlmdbg_cookie2a() is used only in svclock.c.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>