vpp-sflow

Adds egress-sampling and drop-monitoring, bringing into sync with this commit in the main vpp project:
FDio/vpp@8d68794
Note that the drop-monitoring extension depends on the change to vnet/interface_output.c in that commit, so if this release is used to add the latest sFlow plugin to an older version of VPP, then that change will be needed too.

vpp-sflow

This release include a bugfix to the sampling-logic that would have resulted in an undercount at the sFlow collector. The "show err" counters are now updated correctly as well.

vpp-sflow

Bugfix: as detailed in issue #9
Performance improvement - only update the global error-counters periodically from the main thread.

vpp-sflow

Initial release. Ingress packet-sampling and generic counters only.

For standard sFlow export, requires hsflowd version 2.1.10-1 or later to be running locally, compiled with make FEATURES=VPP. See https://github.com/sflow/host-sflow.