asdfasdfasdf
cleanups
bt addresses are strings now
keep fd open, so that MM won't keep reconnecting

NB: Despite it's not wise anyway, there's a bug in the kernel that deferred
rfcomm tty teardown races with the new open. The newly open tty gets a HUP
which confuses NM and the deallocation fails on a refcount check, making the
old rfcomm stuck in the kernel, needing a reboot for another reopen to succeed.
callback