So pcapd on iOS is supposed to allow you to capture packets from a trusted computer: http://support.apple.com/kb/HT6331?viewlocale=en_US&locale=e...

  pcapd supports diagnostic packet capture from an iOS device to a trusted computer. This is useful for troubleshooting and diagnosing issues with apps on the device as well as enterprise VPN connections. You can find more information at developer.apple.com/library/ios/qa/qa1176.

If you actually follow that link, you come out to a page detailing how to do packet captures for different Apple devices, including iOS:

  iOS does not support packet tracing directly. However, if you're developing for iOS you can take a packet trace of your app in a number of different ways:

  If the problem you're trying to debug occurs on Wi-Fi, you can put your iOS device on a test Wi-Fi network. See Wi-Fi Capture for details.
  If your app uses HTTP, you can configure your iOS device to use a debugging HTTP proxy (such as Charles HTTP Proxy).
  In iOS 5 and later you can use the remote virtual interface facility.

There does not seem to be a mention of that pcapd capability in there...