Feature Request: Option to disable masquerade

It would be nice to have an option to disable the default masquerade somehow for both IPv4 and IPv6 #560 is related but focuses specifically on IPv6

Looking at a chain automatically created in my use-case, this 2nd rule is always there, and it would be nice to be able to toggle that on or off.

```
chain NETAVARK-E468CF7D5F9C4 {
ip daddr 100.64.1.0/24 counter packets 7 bytes 1024 accept
ip daddr != 224.0.0.0/4 counter packets 4399 bytes 246472 masquerade
}
```

My understand is Docker allows the user to disable it via a driver option -- `com.docker.network.bridge.enable_ip_masquerade=false`, so something like that would be useful in netarark