Improve handling of received parameters in mod_manager.c

There are commands whose parameters may change settings of the proxy but their processing repeats code and checks only non-default options.  E.g.

```c
if (strcasecmp(key, "Reversed") == 0) {
    if (strcasecmp(val, "yes") == 0) {
        nodeinfo->mess.reversed = 1;
    }
}
```

We should update this approach with some appropriate abstraction covering all options.