[FEATURE] Topology hiding params avp

Hello Everyone, 
Can you please add support of avp for extra parameters in module configuration 

Current param

```
modparam("topology_hiding", "th_passed_contact_params", "paramname1;myparam;custom_param")

```

In script 

```
$avp(myparam) = "realip="  +  $hdr("X-Real-IP); 
```

New param avp

```
modparam("topology_hiding", "th_passed_contact_params", "$avp(myparam)")

```