Add BFD protocol option 'strict bind' to use separate listening socket
for each BFD interface bound to its address instead of using shared
listening sockets.
Direct BFD sessions needs to be dispatched not only by IP addresses, but
also by interfaces, in order to avoid collisions between neighbors with
the same IPv6 link-local addresses.
Extend BFD session hash_ip key by interface index to handle that. Use 0
for multihop sessions.
Thanks to Sebastian Hahn for the original patch.
BFD session options are configured per interface in BFD protocol. This
patch allows to specify them also per-request in protocols requesting
sessions (currently limited to BGP).
Implement BFD authentication (part of RFC 5880). Supports plaintext
passwords and cryptographic MD5 / SHA-1 authentication.
Based on former commit from Pavel Tvrdik
