Switch to new BFD API
This changes the code to use newer APIs available since BFD 2.33 or 2.34 (I'm not entirely sure). I briefly tried to make this backwards-compatible, but ran into some problems. Since this optional utility functionality, I decided to just switch to the new API instead.
Fixes: #391 (closed) Signed-off-by: Uli Schlachter psychon@znc.in