This patch changes BGP from only listening mode for BFD status updates to interactive...

This patch changes BGP from only listening mode for BFD status updates to interactive mode of dynamically registering/deregistering BFD enabled peers with PTM/BFD through zebra. Peer is registered with BFD when it goes into established state and de-registers when it goes out of establish state.

This patch also adds BFD multihop support for BGP. Whether a peer is multi-hop or single hop is determined internally. All IGP peers are considered as multi-hop peers. EBGP peers are considered as single hop unless configured as multi-hop.

BGP BFD command enhancement to configure BFD parameters (detect multiplier, min rx and min tx).

router bgp <as-number>
  neighbor <name/ip-address> bfd <detect mult> <min rx> <min tx>

Signed-off-by: Radhika Mahankali <radhika@cumulusnetworks.com>
Reviewed-by:   Dinesh G Dutt <ddutt@cumulusnetworks.com>
Reviewed-by:   Vipin Kumar <vipin@cumulusnetworks.com>
Reviewed-by:   Kanna Rajagopal <kanna@cumulusnetworks.com>