Implement DTLS support

[lextm]

Both https://www.nuget.org/packages/Waher.Security.DTLS/ and https://www.nuget.org/packages/DTLS.Net/ offer DTLS implementation (server and client), so it is possible now to add DTLS support in #SNMP

1. Use DTLS.NET to implement a new listener binding.
2. Use DTLS.NET to implement new extension methods to send messages.
3. Cherry pick useful bits from Waher.Security.DTLS as it does not rely on Bouncy Castle.

[kdurkin77]

Does this library support SNMP V3 over TLS or is that to be added with the DTLS?

[kdurkin77]

I don't suppose anyone has been planning to add this in soon? It looks like I need to use SNMP v3 over DTLS with certificates and I'm really not finding much online for C# at least

[kdurkin77]

Any tips on getting started with this?

[lextm]

The relevant classes have been moved to the samples repo,

https://github.com/lextudio/sharpsnmplib-samples/tree/master/SharpSnmpLib.Engine/Pipeline

You might write your own Listener/ListenerBinding based on a valid TLS/DTLS implementation, and then things should start to work.

[kdurkin77]

I believe that I am close to getting this implemented, but I'm getting an error "unknown security name". Do you know how to determine the security name to use?

[lextm]

#133 is related to this.