review: th/nm_utils_hwaddr_ntoa_len

[Dan Williams <dcbw redhat com>]

Since there's no bug for it yet...

> core: refactor to use nm_utils_hwaddr_ntoa_len() instead of printf()

Instead of touching nm-device-bt.c, lets just make it super-simple, for
which I pushed a patch.  Although you probably want to rebase and move
the commit earlier and fixup, and then just not touch nm-device-bt.c in
this commit at all.

The rest looks great!

Dan