Netstack (#1403)

Add netstack support for the agent to run it without privileges.

- use interface for tun device
- use common IPC for userspace WireGuard integration
- move udpmux creation and sharedsock to tun layer

iface/iface_linux.go

@@ -0,0 +1,48 @@
+//go:build !android
+// +build !android
+
+package iface
+
+import (
+	"fmt"
+
+	"github.com/pion/transport/v3"
+
+	"github.com/netbirdio/netbird/iface/netstack"
+)
+
+// NewWGIFace Creates a new WireGuard interface instance
+func NewWGIFace(iFaceName string, address string, wgPort int, wgPrivKey string, mtu int, transportNet transport.Net, args *MobileIFaceArguments) (*WGIface, error) {
+	wgAddress, err := parseWGAddress(address)
+	if err != nil {
+		return nil, err
+	}
+
+	wgIFace := &WGIface{}
+
+	// move the kernel/usp/netstack preference evaluation to upper layer
+	if netstack.IsEnabled() {
+		wgIFace.tun = newTunNetstackDevice(iFaceName, wgAddress, wgPort, wgPrivKey, mtu, transportNet, netstack.ListenAddr())
+		wgIFace.userspaceBind = true
+		return wgIFace, nil
+	}
+
+	if WireGuardModuleIsLoaded() {
+		wgIFace.tun = newTunDevice(iFaceName, wgAddress, wgPort, wgPrivKey, mtu, transportNet)
+		wgIFace.userspaceBind = false
+		return wgIFace, nil
+	}
+
+	if !tunModuleIsLoaded() {
+		return nil, fmt.Errorf("couldn't check or load tun module")
+	}
+	wgIFace.tun = newTunUSPDevice(iFaceName, wgAddress, wgPort, wgPrivKey, mtu, transportNet)
+	wgIFace.userspaceBind = true
+	return wgIFace, nil
+
+}
+
+// CreateOnAndroid this function make sense on mobile only
+func (w *WGIface) CreateOnAndroid([]string, string, []string) error {
+	return fmt.Errorf("this function has not implemented on this platform")
+}