ksmbd: Implement new SMB3 POSIX type

As SMB3 posix extension specification, Give posix file type to posix
mode.

https://www.samba.org/~slow/SMB3_POSIX/fscc_posix_extensions.html#posix-file-type-definition



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