Optimized netmap NIOCTXSYNC usage. Can only call when queue is completely empty or completely full - for #28

Restore GSO, TSO and RX/TX checksum offload when restoring adapter to normal mode.
netmap now works with v5 API. Abort will reset netmap interface properly. This closes #28
Merge pull request #29 from appneta/Enhancement_#28_netmap_tuning

Enhancement #28 netmap tuning