ksmbd: downgrade RWH lease caching state to RH for directory

RWH(Read + Write + Handle) caching state is not supported for directory.
ksmbd downgrade it to RH for directory if client send RWH caching lease
state.

Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>