cifs: Accept validate negotiate if server return NT_STATUS_NOT_SUPPORTED
Old windows version or Netapp SMB server will return
NT_STATUS_NOT_SUPPORTED since they do not allow or implement
FSCTL_VALIDATE_NEGOTIATE_INFO. The client should accept the response
provided it's properly signed.
See
https://blogs.msdn.microsoft.com/openspecification/2012/06/28/smb3-secure-dialect-negotiation/