net: TestDialTimeoutFDLeak failure

Fixes #4384.

Implments the suggestion by rsc in comment 15, http://code.google.com/p/go/issues/detail?id=4384#c15

An alternate suggestion would be to temporarily set GOMAXPROCS to 1 during this test.

R=fullung, rsc
CC=golang-dev
https://golang.org/cl/6923046

src/pkg/net/dial_test.go

@@ -240,7 +240,8 @@ func TestDialTimeoutFDLeak(t *testing.T) {
 		err  error
 	}
 	dials := listenerBacklog + 100
-	maxGoodConnect := listenerBacklog + 5 // empirically 131 good ones (of 128). who knows?
+	// used to be listenerBacklog + 5, but was found to be unreliable, issue 4384.
+	maxGoodConnect := 150
 	resc := make(chan connErr)
 	for i := 0; i < dials; i++ {
 		go func() {