Adding ping_ack_timeout in mod_opt_type configuration

Adding ping_ack_timeout in mod_opt_type configuration

Avoid the error output

```
2015-11-18 12:02:40.297 [error] <0.37.0>@gen_mod:validate_opts:250 unknown option 'ping_ack_timeout' for module 'mod_ping' will be likely ignored, available options are: 'iqdisc', 'ping_interval', 'send_pings', 'timeout_action'
2015-11-18 12:02:40.334 [error] <0.37.0>@gen_mod:validate_opts:250 unknown option 'ping_ack_timeout' for module 'mod_ping' will be likely ignored, available options are: 'iqdisc', 'ping_interval', 'send_pings', 'timeout_action'
```

In setting mod_opt_type default, ping_ack_timeout parameter was added.