[client] Add flag to configure MTU (#4213)

client/iface/wgproxy/udp/proxy.go

@@ -12,12 +12,14 @@ import (
 	log "github.com/sirupsen/logrus"
 
 	cerrors "github.com/netbirdio/netbird/client/errors"
+	"github.com/netbirdio/netbird/client/iface/bufsize"
 	"github.com/netbirdio/netbird/client/iface/wgproxy/listener"
 )
 
 // WGUDPProxy proxies
 type WGUDPProxy struct {
 	localWGListenPort int
+	mtu               uint16
 
 	remoteConn net.Conn
 	localConn  net.Conn
@@ -34,10 +36,11 @@ type WGUDPProxy struct {
 }
 
 // NewWGUDPProxy instantiate a UDP based WireGuard proxy. This is not a thread safe implementation
-func NewWGUDPProxy(wgPort int) *WGUDPProxy {
+func NewWGUDPProxy(wgPort int, mtu uint16) *WGUDPProxy {
 	log.Debugf("Initializing new user space proxy with port %d", wgPort)
 	p := &WGUDPProxy{
 		localWGListenPort: wgPort,
+		mtu:               mtu,
 		closeListener:     listener.NewCloseListener(),
 	}
 	return p
@@ -144,7 +147,7 @@ func (p *WGUDPProxy) proxyToRemote(ctx context.Context) {
 		}
 	}()
 
-	buf := make([]byte, 1500)
+	buf := make([]byte, p.mtu+bufsize.WGBufferOverhead)
 	for ctx.Err() == nil {
 		n, err := p.localConn.Read(buf)
 		if err != nil {
@@ -179,7 +182,7 @@ func (p *WGUDPProxy) proxyToLocal(ctx context.Context) {
 		}
 	}()
 
-	buf := make([]byte, 1500)
+	buf := make([]byte, p.mtu+bufsize.WGBufferOverhead)
 	for {
 		n, err := p.remoteConnRead(ctx, buf)
 		if err != nil {