lockd: Relocate include/linux/lockd/lockd.h

lockd: Relocate include/linux/lockd/lockd.h

Headers placed in include/linux/ form part of the kernel's
internal API and signal to subsystem maintainers that other
parts of the kernel may depend on them. By moving lockd.h
into fs/lockd/, lockd becomes a more self-contained module
whose internal interfaces are clearly distinguished from its
public contract with the rest of the kernel. This relocation
addresses a long-standing XXX comment in the header itself
that acknowledged the file's misplacement. Future changes to
lockd internals can now proceed with confidence that external
consumers are not inadvertently coupled to implementation
details.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>