cifs: remove unneeded 2bytes of padding from smb2 tree connect

Due to the 2bytes of padding from the smb2 tree connect request,
there is an unneeded difference between the rfc1002 length and the actual
frame length. In the case of windows client, it is sent by matching it
exactly.

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