nfsd: fix access checking for NLM under XPRTSEC policies

When an export policy with xprtsec policy is set with "tls"
and/or "mtls", but an NFS client is doing a v3 xprtsec=tls
mount, then NLM locking calls fail with an error because
there is currently no support for NLM with TLS.

Until such support is added, allow NLM calls under TLS-secured
policy.

Fixes: 4cc9b9f2 ("nfsd: refine and rename NFSD_MAY_LOCK")
Cc: stable@vger.kernel.org
Signed-off-by: Olga Kornievskaia <okorniev@redhat.com>
Reviewed-by: NeilBrown <neil@brown.name>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>