bgp: use IFMapConfigListener implementation

Previous BgpConfigListener implementation was made abstract in order to reduce
code redundancy.

Change-Id: If3d2564889ff54b077070f39c2a91bc0377d5e05
Signed-off-by: Mateusz Zalega <mateusz.zalega@codilime.com>
Merge "bgp: use IFMapConfigListener implementation"