[client] Add bind activity listener to bypass udp sockets (#4646)

client/iface/device/endpoint_manager.go

@@ -0,0 +1,13 @@
+package device
+
+import (
+	"net"
+	"net/netip"
+)
+
+// EndpointManager manages fake IP to connection mappings for userspace bind implementations.
+// Implemented by bind.ICEBind and bind.RelayBindJS.
+type EndpointManager interface {
+	SetEndpoint(fakeIP netip.Addr, conn net.Conn)
+	RemoveEndpoint(fakeIP netip.Addr)
+}