net/linux: add net_netlink_addrs

[sreimers]

This pull request adds support for obtaining network interface addresses using the RTNETLINK API on Linux systems.

fixes baresip/baresip#3245

[alfredh]

seems to work on Linux:

Local network addresses:
     enp2s0:  10.0.1.2
     enp2s0:  fe80::ea9c:25ff:fe8a:f1fe

[sreimers]

@cspiel1 @maximilianfridrich @juha-h would be nice if you can test this PR too.

[juha-h]

I built baresip app using re of this PR and baresip app on Debian worked OK over WiFi interface.

[maximilianfridrich]

I just tested it with my normal setup and with a setup mimicking @robert-scheck's. Looks good.

PS: I setup a new bridge interface br9 and assigned a tentative IPv6 using sudo ip addr add fd00::1/64 dev br9 tentative. With main branch, it crashed, with this branch, the tentative IPv6 is ignored.

[robert-scheck]

I can't comment about the actual code changes, just about the result: Yes, it solves the problem, thank you :)

[sreimers]

Thanks all for testing and review!