[release-branch.go1.15] net/http: prevent infinite wait during TestMissingStatusNoPanic

If the client request never makes it to the server, the outstanding
accept is never broken. Change the test to always close the listening
socket when the client request completes.

Updates #45358

Change-Id: I744a91dfa11704e7e528163d7669c394e90456dc
Reviewed-on: https://go-review.googlesource.com/c/go/+/319275
Trust: Heschi Kreinick <[email protected]>
Reviewed-by: Bryan C. Mills <[email protected]>
(cherry picked from commit c0a7ecf)
Reviewed-on: https://go-review.googlesource.com/c/go/+/320189
Reviewed-by: Damien Neil <[email protected]>
Run-TryBot: Bryan C. Mills <[email protected]>
Run-TryBot: Damien Neil <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: fraenkel

src/net/http/transport_test.go

@@ -5270,7 +5270,6 @@ func TestMissingStatusNoPanic(t *testing.T) {
 
 	ln := newLocalListener(t)
 	addr := ln.Addr().String()
-	shutdown := make(chan bool, 1)
 	done := make(chan bool)
 	fullAddrURL := fmt.Sprintf("http://%s", addr)
 	raw := "HTTP/1.1 400\r\n" +
@@ -5282,10 +5281,7 @@ func TestMissingStatusNoPanic(t *testing.T) {
 		"Aloha Olaa"
 
 	go func() {
-		defer func() {
-			ln.Close()
-			close(done)
-		}()
+		defer close(done)
 
 		conn, _ := ln.Accept()
 		if conn != nil {
@@ -5316,7 +5312,7 @@ func TestMissingStatusNoPanic(t *testing.T) {
 		t.Errorf("got=%v want=%q", err, want)
 	}
 
-	close(shutdown)
+	ln.Close()
 	<-done
 }