TUN-6191: Update quic-go to v0.27.1 and with custom patch to allow keep alive period to be configurable

The idle period is set to 5sec.

We now also ping every second since last activity.
This makes the quic.Connection less prone to being closed with
no network activity, since we send multiple pings per idle
period, and thus a single packet loss cannot cause the problem.

vendor/github.com/lucas-clemente/quic-go/multiplexer.go

@@ -32,7 +32,7 @@ type connManager struct {
 }
 
 // The connMultiplexer listens on multiple net.PacketConns and dispatches
-// incoming packets to the session handler.
+// incoming packets to the connection handler.
 type connMultiplexer struct {
 	mutex sync.Mutex