vppapigen: api crc checker

crcchecker is a tool for enforcement of the binary API.

1. Production APIs should never change.
2. An API can be deprecated across three release cycles.
   Release 1: API is marked as deprecated.
   option deprecated="vyy.mm";
   option replaced_by="new_api_2";
   Release 2: both old and new APIs are supported
   Release 3: the deprecated API is deleted.
3. APIs that are experimental / not released are not checked.
   An API message can be individually marked as in progress, by:
   option status="in_progress";
   In the API definition.

The definition of a "production API" is if the major version in the API file is > 0.

extras/scripts/crcchecker.py --check-patchset # returns -1 if backwards incompatible
extras/scripts/crcchecker.py --dump-manifest
extras/scripts/crcchecker.py --git-revision v20.01 <files>
extras/scripts/crcchecker.py -- diff <oldfile> <newfile>

This patch integrates the tool in "make checkstyle-api".
A future patch is required to integrate the tool in the verify job.
I.e. this patch does not enable enforcement through Jenkins.

Change-Id: I5f13c0976d8a12a58131b3e270f2dc9c00dc7d8c
Type: feature
Signed-off-by: Ole Troan <ot@cisco.com>

Makefile

@@ -227,6 +227,7 @@ help:
 	@echo " checkstyle           - check coding style"
 	@echo " checkstyle-commit    - check commit message format"
 	@echo " checkstyle-test      - check test framework coding style"
+	@echo " checkstyle-api       - check api for incompatible changes"
 	@echo " fixstyle             - fix coding style"
 	@echo " doxygen              - (re)generate documentation"
 	@echo " bootstrap-doxygen    - setup Doxygen dependencies"
@@ -677,6 +678,10 @@ checkstyle-all: checkstyle-commit checkstyle checkstyle-test
 fixstyle:
 	@build-root/scripts/checkstyle.sh --fix
 
+.PHONY: checkstyle-api
+checkstyle-api:
+	@extras/scripts/crcchecker.py --check-patch
+
 # necessary because Bug 1696324 - Update to python3.6 breaks PyYAML dependencies
 # Status:	CLOSED CANTFIX
 # https://bugzilla.redhat.com/show_bug.cgi?id=1696324