Update usage of Wintun, avoid disconnections on Windows

Fixes #338 (closed)

Start by following the example in Wintun 10.2 and 0.13 to the letter:

• Always call WintunReleaseReceivePacket() after WintunReceivePacket(), even if the packet is dropped due to exceeding the tunnel MTU.
• Extended logging with GetLastError().
• Clean up adapters as in the Wintun example:
  https://github.com/WireGuard/wintun/blob/73a4cffee083e3fdfa4143590d01e51e0f63c9f0/example/example.c#L392-L394

  cleanupAdapter:
      WintunDeleteAdapter(Adapter, FALSE, NULL);
      WintunFreeAdapter(Adapter);

Then fix the actual errors in our code.