bfd: schema: added IETF BFD as defined in RFC5880

Change-Id: Iffba8ee97309a5342c965c542fdf25238801db39
Signed-off-by: Mateusz Zalega <mateusz.zalega@codilime.com>
Merge "bfd: schema: added IETF BFD as defined in RFC5880"