fix: disable the whole underload if DisableCookies is on

Thanks to @darkk for spotting and suggesting the fix

device/receive.go

@@ -369,7 +369,8 @@ func (device *Device) RoutineHandshake(id int) {
 
 			// endpoints destination address is the source of the datagram
 
-			if device.IsUnderLoad() {
+			disableCookies := device.disableCookies.Load()
+			if !disableCookies && device.IsUnderLoad() {
 
 				// verify MAC2 field
 

device/send.go

@@ -239,11 +239,6 @@ func (peer *Peer) SendHandshakeResponse() error {
 }
 
 func (device *Device) SendHandshakeCookie(initiatingElem *QueueHandshakeElement) error {
-	if device.disableCookies.Load() {
-		device.log.Verbosef("Sending cookie response blocked for %v due to disabled cookies", initiatingElem.endpoint.DstToString())
-		return nil
-	}
-
 	device.log.Verbosef("Sending cookie response for denied handshake message for %v", initiatingElem.endpoint.DstToString())
 
 	sender := binary.LittleEndian.Uint32(initiatingElem.packet[4:8])