fix(netxlite/dns): more stricly mirror stdlib error strings (#513)

This diff attempts to modify the errors reported by our custom
resolver by matching more strings from the stdlib.

Part of https://github.com/ooni/probe/issues/1733 and diff has been
extracted from https://github.com/ooni/probe-cli/pull/506.

internal/netxlite/resolver_test.go

@@ -146,12 +146,18 @@ func TestResolverLogger(t *testing.T) {
 				},
 			}
 			expected := []string{"1.1.1.1"}
-			r := resolverLogger{
+			r := &resolverLogger{
 				Logger: lo,
 				Resolver: &mocks.Resolver{
 					MockLookupHost: func(ctx context.Context, domain string) ([]string, error) {
 						return expected, nil
 					},
+					MockNetwork: func() string {
+						return "system"
+					},
+					MockAddress: func() string {
+						return ""
+					},
 				},
 			}
 			addrs, err := r.LookupHost(context.Background(), "dns.google")
@@ -174,12 +180,18 @@ func TestResolverLogger(t *testing.T) {
 				},
 			}
 			expected := errors.New("mocked error")
-			r := resolverLogger{
+			r := &resolverLogger{
 				Logger: lo,
 				Resolver: &mocks.Resolver{
 					MockLookupHost: func(ctx context.Context, domain string) ([]string, error) {
 						return nil, expected
 					},
+					MockNetwork: func() string {
+						return "system"
+					},
+					MockAddress: func() string {
+						return ""
+					},
 				},
 			}
 			addrs, err := r.LookupHost(context.Background(), "dns.google")