shouldBlockRequest: Don't block if socket connect fails

* On (re)boot:

  05-19 13:27:49.303   605   987 I netd    : DnsResolverService::setResolverConfiguration(100, [192.168.1.1], [], 1800, 25, 8, 64, 0, 0, [], []) -> (-22) (0.6ms)
  05-19 13:27:49.303   605   987 I netd    : setResolverConfiguration() -> ServiceSpecificException(22, "Invalid argument") <1.35ms>
  05-19 13:27:49.304  1574  1698 E DnsManager: Error setting DNS configuration: android.os.ServiceSpecificException: Invalid argument (code 22)

  ..which subsequently leads to connectivity check probes failing.

* Thanks to Alexandre for the hint