socket-exists requires cmd-owner

While [iptables-extensions.man](https://ipset.netfilter.org/iptables-extensions.man.html#lbBP) says `socket-exists` should be used the same as `uid-owner` or `uid-owner`, ferm requires and inserts `cmd-owner` before.

```
chain OUTPUT mod owner socket-exists <--
Unrecognized keyword: socket-exists
```