It says on top to put SMPP server there. So, you should put your sms service provider's smpp address there.
Offtopic: my god, why have someone translated the name of Openfire, literally
IP address of the login port with the password specified is correct.
It is necessary to specify source address, the only question is where to specify this parameter.
Openfires Admin Console provides a user interface only for the most common settings for SMPP. You can, however, set a lot more options, by specifying them via properties. The source address is one of those.
This comment in the source code lists all settings that are supported, and what the corresponding property names are: Openfire/SmsService.java at master · igniterealtime/Openfire · GitHub