feat: allow setting listen address explicitly

[Pandapip1]

This allows for the address to be set explicitly, for applications which would prefer to set their own addresses without using the config file.

WIP; currently in the process of being tested

[cboulay]

Hi @Pandapip1 ,

Believe me, I would love this feature. It would fix a bunch of headaches for me. However, I am extremely reluctant to change the API surface like this, especially when it's something that can be handled with the config file (and possibly requiring #278 and #279). Would runtime config changing then be enough?

liblsl's API changes slowly and that's on purpose. There are manufacturers and government agencies who use liblsl in various capacities at least in-part because it is stable.

I realize that this proposed change does not break the existing API. I'm more concerned about putting out a release with this change then discovering some fundamental problem (e.g., related to security which is an increasing concern) and then we have to break the API to remove this.

I'm happy to leave this PR open for a while (indefinitely) for public comment.

Cheers,
Chad

[Pandapip1]

Thanks for the early comment; if this is something that's unlikely to be accepted then I'll be prioritizing working on and testing some other things. I'll close this PR but I'll keep the branch; if anyone wants to fork from it they should free to do so.