[release-branch.go1.21] net: tolerate permission errors in interface tests

On our linux-arm64 builders, we're getting permission errors despite
running as root. Detect those errors and skip the test.

Fixes #61414.

Change-Id: I5d7c45789337bee3860b19335bbb9eb884c48986
Reviewed-on: https://go-review.googlesource.com/c/go/+/510737
Auto-Submit: Heschi Kreinick <[email protected]>
Run-TryBot: Heschi Kreinick <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
(cherry picked from commit 8e1ec1c)
Reviewed-on: https://go-review.googlesource.com/c/go/+/511136
Reviewed-by: Dmitri Shuralyov <[email protected]>
TryBot-Bypass: Dmitri Shuralyov <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: heschi

src/net/interface_unix_test.go

@@ -193,6 +193,9 @@ func TestInterfaceArrivalAndDepartureZoneCache(t *testing.T) {
 		t.Skipf("test requires external command: %v", err)
 	}
 	if err := ti.setup(); err != nil {
+		if e := err.Error(); strings.Contains(e, "Permission denied") {
+			t.Skipf("permission denied, skipping test: %v", e)
+		}
 		t.Fatal(err)
 	}
 	defer ti.teardown()