Display packet drop stats

[twood02]

Feature Request

We should display statistics about how many packets are dropped by the NIC before they reach the manager.

We can get the stats here: https://doc.dpdk.org/api/structrte__event__eth__rx__adapter__stats.html#a7c2f568a81a574e072c66a0246044d56

This should be displayed as part of the manager's stats thread loop:
https://github.com/sdnfv/openNetVM/blob/master/onvm/onvm_mgr/onvm_stats.c#L313
You'll need to update the definitions found in:
https://github.com/sdnfv/openNetVM/blob/master/onvm/onvm_mgr/onvm_stats.h#L85-L87

[strongcourage]

Hi, I made this pull request #311. Thanks.