Make use of .NET 6 new socket API such as cancelation token support

[lextm]

.NET 6 finally introduces new socket API such as Socket.SendToAsync with cancelation token support,

https://docs.microsoft.com/en-us/dotnet/api/system.net.sockets.socket.sendtoasync?view=net-6.0#System_Net_Sockets_Socket_SendToAsync_System_ReadOnlyMemory_System_Byte__System_Net_Sockets_SocketFlags_System_Net_EndPoint_System_Threading_CancellationToken_

#SNMP Library can added new methods to adapt to such changes.

#140 is only one of the scenarios.

[zivillian]

I've created a first draft of an implementation which should work on all supported platforms.

zivillian@6c71154

The SocketExtension implementation can later be made platform dependent to use the native implementation for net6.

What do you think? Should I complete the implementation and add the remaining overloads and CancellationToken parameter?

[lextm]

@zivillian It looks nice, and I start to wonder if we should ship the newly implemented methods in a separate library (NuGet package). The benefit of a separate package is that we can explicitly mark it as .NET 6 and above only (instead of adding conditional compilation in the current library).

[lextm]

Is being worked in https://github.com/lextudio/sharpsnmplib/tree/net6

[lextm]

Implemented in recent commits.