libtins: Don't throw exception on invalid interface

[someburner]

Issue template (remove lines from top till here)

Environment: openwrt 23.05.5 maybe others, likely all archs

Description:

This library throws an exception when an "invalid interface" is seen, which it defines as having no ip address and no mac address. But I believe this is the case for certain interfaces, like vpn ifs.

The simple workaround is to just comment out the exception, and everything works fine.

I made a patch here:
https://github.com/someburner/openwrt-feeds/blob/master/libtins45/patches/011-no-throw-empty-iface.patch

But figured I'd make an issue first.