fix(admission): use client network, fail-open on nil gRPC client, close http resources

- Use client address network instead of listener network in admission wrapper
- Return true (allow) when gRPC admission plugin client is nil to fail-open
- Add Close() to httpPlugin to close idle HTTP connections
- Close httpLoader in localAdmission.Close()
- Remove dead commented-out code in periodReload

admission/plugin/http.go

@@ -91,3 +91,10 @@ func (p *httpPlugin) Admit(ctx context.Context, network, addr string, opts ...ad
 	}
 	return res.OK
 }
+
+func (p *httpPlugin) Close() error {
+	if p.client != nil {
+		p.client.CloseIdleConnections()
+	}
+	return nil
+}