hack: re-enable protobindings which use k8s.io/api

Before the workspace changes, it was possible to include proto files via the
vendor path and the symlinks there. Now those symlinks are gone, so the search
path for them must be given separately.

hack/lib/protoc.sh

@@ -69,6 +69,7 @@ function kube::protoc::protoc() {
     PATH="${gogopath}:${PATH}" protoc \
       --proto_path="$(pwd -P)" \
       --proto_path="${KUBE_ROOT}/vendor" \
+      --proto_path="${KUBE_ROOT}/staging/src" \
       --proto_path="${KUBE_ROOT}/third_party/protobuf" \
       --gogo_out=paths=source_relative,plugins=grpc:. \
       api.proto