cifs: remove useless parameter 'is_fsctl' from SMB2_ioctl()

SMB2_ioctl() is always called with is_fsctl = true, so doesn't make any
sense to have it at all.

Thus, always set SMB2_0_IOCTL_IS_FSCTL flag on the request.

Also, as per MS-SMB2 3.3.5.15 "Receiving an SMB2 IOCTL Request", servers
must fail the request if the request flags is zero anyway.

Signed-off-by: Enzo Matsumiya <ematsumiya@suse.de>
Reviewed-by: Tom Talpey <tom@talpey.com>
Signed-off-by: Steve French <stfrench@microsoft.com>