Script to list patches that changed api files.

- Add Ole Troan's script from vpp-dev email:
  https://lists.fd.io/pipermail/vpp-dev/2017-October/007037.html

Change-Id: I0cbf5118169dc25f0edd659a5a9f5cde8619f780
Signed-off-by: Dave Wallace <dwallacelf@gmail.com>

extras/scripts/list_api_changes.py

@@ -0,0 +1,15 @@
+#!/usr/bin/env python
+import os, fnmatch, subprocess
+starttag = 'v18.01-rc0'
+endtag = 'v18.01-rc2'
+apifiles = []
+for root, dirnames, filenames in os.walk('.'):
+    for filename in fnmatch.filter(filenames, '*.api'):
+        apifiles.append(os.path.join(root, filename))
+for f in apifiles:
+    commits = subprocess.check_output(['git', 'log',
+                                       '--oneline', starttag + '..' + endtag,
+                                       f])
+    if commits:
+        print f
+        print commits