Unhandled exception when UdpSocket is disposed but inner disposed socket receives an input

[gelexgaray]

on public System.Threading.Tasks.Task ReceiveAsync()

When the UdpSocket is disposed and the inner socket is also disposed, ReceiveAsync raises a DisposedException on network input. It shouldn't raise any exception in this case.

This is managed in the NETSTANDARD1.3 code, but not in the rest of the variants of the code

I will send you a pull request with a fix proposal