rename files dealing with low level conns to sys_conn

sys_conn_helper_linux.go

@@ -0,0 +1,20 @@
+//go:build linux
+// +build linux
+
+package quic
+
+import "golang.org/x/sys/unix"
+
+const msgTypeIPTOS = unix.IP_TOS
+
+const (
+	ipv4RECVPKTINFO = unix.IP_PKTINFO
+	ipv6RECVPKTINFO = unix.IPV6_RECVPKTINFO
+)
+
+const (
+	msgTypeIPv4PKTINFO = unix.IP_PKTINFO
+	msgTypeIPv6PKTINFO = unix.IPV6_PKTINFO
+)
+
+const batchSize = 8 // needs to smaller than MaxUint8 (otherwise the type of oobConn.readPos has to be changed)