Have you tried making a custom App ID for this? ICMP type 3 is not one of the App ID signatures in the native database, but it looks like it would be easy to create one. I did it quickly and you can see it in the attached screen capture, but I haven't tested it. Maybe you could give it a shot!
To create a custom App ID, go to Objects tab > Applications > Click the "New" button. Give it a name and description in the "Configuration" tab, and then in the "Advanced" tab, you can choose your ICMP type.
Once you have a custom App ID, you could create a security policy to allow this application.
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