smb3: negotiate current dialect (SMB3.1.1) when version 3 or greater requested

SMB3.1.1 is the newest, and preferred dialect, and is included in
the requested dialect list by default (ie if no vers= is specified
on mount) but it should also be requested if SMB3 or later is requested
(vers=3 instead of a specific dialect: vers=2.1, vers=3.02 or vers=3.0).

Currently specifying "vers=3" only requests smb3.0 and smb3.02 but this
patch fixes it to also request smb3.1.1 dialect, as it is the newest
and most secure dialect and is a "version 3 or later" dialect (the intent
of "vers=3").

Signed-off-by: Steve French <stfrench@microsoft.com>
Suggested-by: Pavel Shilovsky <pshilov@microsoft.com>
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>