TUN-4597: Add a QUIC server skeleton

- Added a QUIC server to accept streams
- Unit test for this server also tests ALPN
- Temporary echo capability for HTTP ConnectionType

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

@@ -0,0 +1,17 @@
+// +build darwin
+
+package quic
+
+import "golang.org/x/sys/unix"
+
+const msgTypeIPTOS = unix.IP_RECVTOS
+
+const (
+	ipv4RECVPKTINFO = unix.IP_RECVPKTINFO
+	ipv6RECVPKTINFO = 0x3d
+)
+
+const (
+	msgTypeIPv4PKTINFO = unix.IP_PKTINFO
+	msgTypeIPv6PKTINFO = 0x2e
+)