Hardware-assisted inline BFD

We support a hardware implementation of the inline BFD protocol in firmware form. The ASIC firmware handles most of the BFD protocol processing. The firmware uses existing paths to forward any BFD events that must be processed by protocol processes. The ASIC firmware processes the packets more quickly than the software, so hardware-assisted inline BFD sessions can have keepalive intervals of less than a second. These platforms support this feature for single-hop and multihop IPv4 and IPv6 BFD sessions.