lockd: update nlm_lookup_file reexport comment

[ Upstream commit b661601a ]

Update comment to reflect that we *do* allow reexport, whether it's a
good idea or not....

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>