bugfix in SEALKEY()

[NtAlexio2]

This PR fixes a bug found in ntlm.py which calculates invalid seal key for connection-less sessions in smb.
More information can found in MSDN documentations here.

[anadrianmanrique]

Thanks for the PR @NtAlexio2.
Any tip/suggestion on how to test these changes would be more than appreciated, thanks!

[NtAlexio2]

Let's review added flags:

1. NTLMSSP_NEGOTIATE_LM_KEY: This flag disabled by default on Windows Vista and Server 2008. To enable and test this flag you can check MSDN documents
2. NTLMSSP_NEGOTIATE_DATAGRAM: I'm not sure about scenarios/applications for this one, but you can check documentations here for more information.
3. NTLMSSP_REVISION_W2K3: Setting this revision level indicates compatibility with features and behaviors introduced in Windows Server 2003. So we should test this one by authenticating against Windows Server 2003.

As a short answer just authenticate to Windows Server 2003. Actually this PR improves backward compatibility.