bug: switch to socket.Dup in eventloop.enroll to enable close-on-exec (#745)

Author: panjf2000

client_unix.go

@@ -210,9 +210,7 @@ func (cli *Client) EnrollContext(c net.Conn, ctx any) (Conn, error) {
 
 	var dupFD int
 	e := rc.Control(func(fd uintptr) {
-		dupFD, err = unix.Dup(int(fd))
-		// Set the socket to close-on-exec, so that the socket is closed when the process forks
-		unix.CloseOnExec(dupFD)
+		dupFD, err = socket.Dup(int(fd))
 	})
 	if err != nil {
 		return nil, err

eventloop_unix.go

@@ -139,7 +139,7 @@ func (el *eventloop) enroll(c net.Conn, addr net.Addr, ctx any) (resCh chan Regi
 
 		var dupFD int
 		err1 := rc.Control(func(fd uintptr) {
-			dupFD, err = unix.Dup(int(fd))
+			dupFD, err = socket.Dup(int(fd))
 		})
 		if err != nil {
 			resCh <- RegisteredResult{Err: err}