Add vnet to SettingEngine

Also add simple example to show usage

Resolves #778

examples/vnet/show-network-usage/main.go

@@ -0,0 +1,78 @@
+package main
+
+import (
+	"time"
+
+	"github.com/pion/logging"
+	"github.com/pion/transport/vnet"
+	"github.com/pion/webrtc/v2"
+)
+
+func main() {
+	wan, err := vnet.NewRouter(&vnet.RouterConfig{
+		CIDR:          "1.2.3.0/24",
+		LoggerFactory: logging.NewDefaultLoggerFactory(),
+	})
+	panicIfError(err)
+
+	offerVNet := vnet.NewNet(&vnet.NetConfig{})
+	panicIfError(wan.AddNet(offerVNet))
+
+	offerSettingEngine := webrtc.SettingEngine{}
+	offerSettingEngine.SetVNet(offerVNet)
+	offerAPI := webrtc.NewAPI(webrtc.WithSettingEngine(offerSettingEngine))
+
+	answerVNet := vnet.NewNet(&vnet.NetConfig{})
+	panicIfError(wan.AddNet(answerVNet))
+
+	answerSettingEngine := webrtc.SettingEngine{}
+	answerSettingEngine.SetVNet(answerVNet)
+	answerAPI := webrtc.NewAPI(webrtc.WithSettingEngine(answerSettingEngine))
+
+	panicIfError(wan.Start())
+
+	offerPeerConnection, err := offerAPI.NewPeerConnection(webrtc.Configuration{})
+	panicIfError(err)
+
+	answerPeerConnection, err := answerAPI.NewPeerConnection(webrtc.Configuration{})
+	panicIfError(err)
+
+	offerDataChannel, err := offerPeerConnection.CreateDataChannel("label", nil)
+	panicIfError(err)
+
+	msgSendLoop := func(dc *webrtc.DataChannel) {
+		for {
+			time.Sleep(500 * time.Millisecond)
+			panicIfError(dc.SendText("My DataChannel Message"))
+		}
+
+	}
+
+	offerDataChannel.OnOpen(func() {
+		msgSendLoop(offerDataChannel)
+	})
+
+	answerPeerConnection.OnDataChannel(func(answerDataChannel *webrtc.DataChannel) {
+		answerDataChannel.OnOpen(func() {
+			msgSendLoop(answerDataChannel)
+		})
+	})
+
+	offer, err := offerPeerConnection.CreateOffer(nil)
+	panicIfError(err)
+	panicIfError(offerPeerConnection.SetLocalDescription(offer))
+	panicIfError(answerPeerConnection.SetRemoteDescription(offer))
+
+	answer, err := answerPeerConnection.CreateAnswer(nil)
+	panicIfError(err)
+	panicIfError(answerPeerConnection.SetLocalDescription(answer))
+	panicIfError(offerPeerConnection.SetRemoteDescription(answer))
+
+	select {}
+}
+
+func panicIfError(err error) {
+	if err != nil {
+		panic(err)
+	}
+}