Offload detect

This patchset is a Linux only implementation of offloading detection. It uses ioctl to get the status of GRO and LRO and displays a warning if they are activated when suricata is using AF_PACKET and pcap capture.

This should fix https://redmine.openinfosecfoundation.org/issues/944.

First patch is a bit off topic and fixes https://redmine.openinfosecfoundation.org/issues/943.

PR build: https://buildbot.suricata-ids.org/builders/regit/builds/50