rename files dealing with low level conns to sys_conn

sys_conn_helper_darwin.go

@@ -0,0 +1,22 @@
+//go:build darwin
+// +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
+)
+
+// ReadBatch only returns a single packet on OSX,
+// see https://godoc.org/golang.org/x/net/ipv4#PacketConn.ReadBatch.
+const batchSize = 1