Fix usage of point 2 point devices

[pacho2]

We got this downstream report some time ago:
https://bugs.gentoo.org/show_bug.cgi?id=528722

When activating avahi for point 2 point devices (tun/tap) the daemon uses the destination address instead the local device address.

To fix that, the user provided the following patch... then, it would be nice if it could be reviewed by upstream and accepted if it's really ok. Thanks a lot:
https://528722.bugs.gentoo.org/attachment.cgi?id=388928

[lathiat]

We applied a patch for this already in 8b3f8e4, though this patch goes about it in a different way.

I'll check to ensure it's working as expected.

[pacho2]

Nice, thanks a lot for taking care :)