Add CRC checking in frame2kafka + add adjustable CRC checker backend
This MR refactors some of the CRC checking to allow this to be used end-to-end in both frame2kafka
and kafka2frame
.
In addition, this adds an Fd-based CRC checker from code that was living in igwn-lldd-fdio
pointed out in #5. The way the CRC checks work now is that you can select either a GDS or Fd backend, or select auto (set by default) which selects one based on what is currently installed.