[endpoint1] - [proxy1] - [proxy2] - [endpoint2]

The datapath currently makes the following assumption:

        orig_was_proxy = ip4->saddr == IPV4_GATEWAY;

The meaning of this bool is to indicate whether this is a reply packet that came from the proxy.

This is wrong if:

• the source is a local process on the local host other than the proxy
• the source is an egress proxy sending to another local endpoint