[client] Fix/v4 stun routing (#4430)

Deduplicate STUN package sending.
Originally, because every peer shared the same UDP address, the library could not distinguish which STUN message was associated with which candidate. As a result, the Pion library responded from all candidates for every STUN message.

client/iface/bind/udp_mux_generic.go

@@ -1,22 +0,0 @@
-//go:build !ios
-
-package bind
-
-import (
-	nbnet "github.com/netbirdio/netbird/util/net"
-)
-
-func (m *UDPMuxDefault) notifyAddressRemoval(addr string) {
-	// Kernel mode: direct nbnet.PacketConn (SharedSocket wrapped with nbnet)
-	if conn, ok := m.params.UDPConn.(*nbnet.PacketConn); ok {
-		conn.RemoveAddress(addr)
-		return
-	}
-
-	// Userspace mode: UDPConn wrapper around nbnet.PacketConn
-	if wrapped, ok := m.params.UDPConn.(*UDPConn); ok {
-		if conn, ok := wrapped.GetPacketConn().(*nbnet.PacketConn); ok {
-			conn.RemoveAddress(addr)
-		}
-	}
-}