add a method to the sendQueue to send probe packets (#4939)

send_queue.go

@@ -1,9 +1,14 @@
 package quic
 
-import "github.com/quic-go/quic-go/internal/protocol"
+import (
+	"net"
+
+	"github.com/quic-go/quic-go/internal/protocol"
+)
 
 type sender interface {
 	Send(p *packetBuffer, gsoSize uint16, ecn protocol.ECN)
+	SendProbe(*packetBuffer, net.Addr)
 	Run() error
 	WouldBlock() bool
 	Available() <-chan struct{}
@@ -57,6 +62,10 @@ func (h *sendQueue) Send(p *packetBuffer, gsoSize uint16, ecn protocol.ECN) {
 	}
 }
 
+func (h *sendQueue) SendProbe(p *packetBuffer, addr net.Addr) {
+	h.conn.WriteTo(p.Data, addr)
+}
+
 func (h *sendQueue) WouldBlock() bool {
 	return len(h.queue) == sendQueueCapacity
 }