[release-1.24] codegen: fix DeepCopy races (#2339)

* codegen: fix DeepCopy races

Fixes istio/api#3019

The deepcopygen we use is from Kubernetes. Its not quite suitable for
our types due to our usage of protobuf, which has limitations on
dereferencing pointer types. This causes race conditions in concurrent
usage of the DeepCopy function.

This is possible to trigger with real Istio (found by running Istio in a
live cluster with `-race`, though our current tests happen to not
trigger things I guess), as well as other usage of istio/client-go (as
the reporter found).

I ran istio/istio with this change and found all tests continue to pass,
and running in a live cluster no longer fails

* clarify comments

---------

Co-authored-by: John Howard <john.howard@solo.io>

Makefile.core.mk

@@ -100,6 +100,12 @@ rename_generated_files=\
 	find $(subst istio.io/client-go/, $(empty), $(subst $(comma), $(space), $(kube_api_packages)) $(kube_clientset_package) $(kube_listers_package) $(kube_informers_package)) \
 	-name '*.go' -and -not -name 'doc.go' -and -not -name '*.gen.go' -type f -exec sh -c 'mv "$$1" "$${1%.go}".gen.go' - '{}' \;
 
+# Kubernetes deepcopy gen directly sets values of our types. Our types are protos; it is illegal to do this for protos.
+# However, we don't even need this anyways -- each individual field is explicitly copied already.
+# Remove the line doing this illegal operation.
+fixup_generated_files=\
+	find . -name "*.deepcopy.gen.go" -type f | xargs sed -i -e '/\*out = \*in/d'
+
 .PHONY: generate-k8s-client
 generate-k8s-client:
 	# generate kube api type wrappers for istio types
@@ -117,6 +123,7 @@ generate-k8s-client:
 	@$(informer_gen) --input-dirs $(kube_api_packages) --versioned-clientset-package $(kube_clientset_package)/$(kube_clientset_name) --listers-package $(kube_listers_package) --output-package $(kube_informers_package) -h $(kube_go_header_text)
 	@$(move_generated)
 	@$(rename_generated_files)
+	@$(fixup_generated_files)
 
 .PHONY: build-k8s-client verify-k8s-client
 build-k8s-client: