pfring: fixes small bug

This PR fixes two small bug for pfring.

Bug [#1292](https://redmine.openinfosecfoundation.org/issues/1292)
Bug [#1301](https://redmine.openinfosecfoundation.org/issues/1301)

- PR build: https://buildbot.openinfosecfoundation.org/builders/glongo/builds/12
- PR pcaps: https://buildbot.openinfosecfoundation.org/builders/glongo-pcap/builds/12