tools: add cocci patch for thread cancel api changes

Add Quentin's cocci patch to align code with the changes
to the event cancel api. Also added a README to explain what
this collection of cocci patches is for.

Signed-off-by: Quentin Young <qlyoung@nvidia.com>
Signed-off-by: Mark Stapp <mjs@voltanet.io>

tools/coccinelle/README.md

@@ -0,0 +1,14 @@
+Coccinelle patches
+==================
+
+This collection of coccinelle patches represents some of the broader,
+codebase-wide changes that have been made. If you maintain a fork of
+FRR and find that your codebase needs to be updated to align with
+these changes, the coccinelle tool should help you make that update.
+
+The coccinelle tool is documented at:
+    https://coccinelle.gitlabpages.inria.fr/website/
+
+To run a coccinelle patch script:
+
+    spatch --sp-file tools/coccinelle/semicolon.cocci zebra/*.c

tools/coccinelle/thread_cancel_api.cocci

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+@ptrupdate@
+expression E;
+@@
+- thread_cancel(E);
++ thread_cancel(&E);
+
+@nullcheckremove depends on ptrupdate@
+expression E;
+@@
+
+thread_cancel(&E);
+- E = NULL;
+
+@cancelguardremove depends on nullcheckremove@
+expression E;
+@@
+- if (E)
+- {
+   thread_cancel(&E);
+- }
+
+@cancelguardremove2 depends on nullcheckremove@
+expression E;
+@@
+- if (E != NULL)
+- {
+   thread_cancel(&E);
+- }
+
+@cancelguardremove3 depends on nullcheckremove@
+expression E;
+@@
+- if (E)
+   thread_cancel(&E);
+
+@cancelguardremove4 depends on nullcheckremove@
+expression E;
+@@
+- if (E != NULL)
+   thread_cancel(&E);
+
+@replacetimeroff@
+expression E;
+@@
+
+- THREAD_TIMER_OFF(E);
++ thread_cancel(&E);
+
+@replacewriteoff@
+expression E;
+@@
+
+- THREAD_WRITE_OFF(E);
++ thread_cancel(&E);
+
+@replacereadoff@
+expression E;
+@@
+
+- THREAD_READ_OFF(E);
++ thread_cancel(&E);
+
+@replacethreadoff@
+expression E;
+@@
+
+- THREAD_OFF(E);
++ thread_cancel(&E);