net: skip TestLookupPort on android with netgo

/etc/services is not available on Android. The pure Go implementation
of LookupPort will never succeed on Android. Skipping the test.

Updates #14576.

Change-Id: I707ac24aea3f988656b95b1816ee5c9690106985
Reviewed-on: https://go-review.googlesource.com/20154Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/lookup_test.go

@@ -624,6 +624,10 @@ func TestLookupPort(t *testing.T) {
 	switch runtime.GOOS {
 	case "nacl":
 		t.Skipf("not supported on %s", runtime.GOOS)
+	case "android":
+		if netGo {
+			t.Skipf("not supported on %s without cgo; see golang.org/issues/14576", runtime.GOOS)
+		}
 	}
 
 	for _, tt := range lookupPortTests {