Bind implementation (#779)

This PR adds supports for the WireGuard userspace implementation
using Bind interface from wireguard-go. 
The newly introduced ICEBind struct implements Bind with UDPMux-based
structs from pion/ice to handle hole punching using ICE.
The core implementation was taken from StdBind of wireguard-go.

The result is a single WireGuard port that is used for host and server reflexive candidates. 
Relay candidates are still handled separately and will be integrated in the following PRs.

ICEBind checks the incoming packets for being STUN or WireGuard ones
and routes them to UDPMux (to handle hole punching) or to WireGuard  respectively.

client/internal/stdnet/discover_mobile.go

@@ -0,0 +1,95 @@
+package stdnet
+
+import (
+	"fmt"
+	"net"
+	"strings"
+
+	"github.com/pion/transport/v2"
+	log "github.com/sirupsen/logrus"
+)
+
+type mobileIFaceDiscover struct {
+	externalDiscover ExternalIFaceDiscover
+}
+
+func newMobileIFaceDiscover(externalDiscover ExternalIFaceDiscover) *mobileIFaceDiscover {
+	return &mobileIFaceDiscover{
+		externalDiscover: externalDiscover,
+	}
+}
+
+func (m *mobileIFaceDiscover) iFaces() ([]*transport.Interface, error) {
+	ifacesString, err := m.externalDiscover.IFaces()
+	if err != nil {
+		return nil, err
+	}
+	interfaces := m.parseInterfacesString(ifacesString)
+	return interfaces, nil
+}
+
+func (m *mobileIFaceDiscover) parseInterfacesString(interfaces string) []*transport.Interface {
+	ifs := []*transport.Interface{}
+
+	for _, iface := range strings.Split(interfaces, "\n") {
+		if strings.TrimSpace(iface) == "" {
+			continue
+		}
+
+		fields := strings.Split(iface, "|")
+		if len(fields) != 2 {
+			log.Warnf("parseInterfacesString: unable to split %q", iface)
+			continue
+		}
+
+		var name string
+		var index, mtu int
+		var up, broadcast, loopback, pointToPoint, multicast bool
+		_, err := fmt.Sscanf(fields[0], "%s %d %d %t %t %t %t %t",
+			&name, &index, &mtu, &up, &broadcast, &loopback, &pointToPoint, &multicast)
+		if err != nil {
+			log.Warnf("parseInterfacesString: unable to parse %q: %v", iface, err)
+			continue
+		}
+
+		newIf := net.Interface{
+			Name:  name,
+			Index: index,
+			MTU:   mtu,
+		}
+		if up {
+			newIf.Flags |= net.FlagUp
+		}
+		if broadcast {
+			newIf.Flags |= net.FlagBroadcast
+		}
+		if loopback {
+			newIf.Flags |= net.FlagLoopback
+		}
+		if pointToPoint {
+			newIf.Flags |= net.FlagPointToPoint
+		}
+		if multicast {
+			newIf.Flags |= net.FlagMulticast
+		}
+
+		ifc := transport.NewInterface(newIf)
+
+		addrs := strings.Trim(fields[1], " \n")
+		foundAddress := false
+		for _, addr := range strings.Split(addrs, " ") {
+			ip, ipNet, err := net.ParseCIDR(addr)
+			if err != nil {
+				log.Warnf("%s", err)
+				continue
+			}
+			ipNet.IP = ip
+			ifc.AddAddress(ipNet)
+			foundAddress = true
+		}
+		if foundAddress {
+			ifs = append(ifs, ifc)
+		}
+	}
+	return ifs
+}