[swss]: BFD hardware offload for BGP sessions

[baorliu]

What I did using hardware offloaded BFD to replace frr/bfdd for BGP neighbor reachability detection.

Why I did it Hardware offloaded BFD usually provide more bfd sessions support, and has shorter detection time comparing to software bfd. and also lower CPU load because that BFD sessions are offloaded to hardware/ASIC.

How I verified it The design was built into a sonic image, and verified in a hardware testbed.

Details if related This program is built under sonic-swss, but running in bgp container.

HLD in PR review: https://github.com/sonic-net/SONiC/pull/1599