Seamless BFD (S-BFD)

[j-bos]

Seamless Bidirectional Forwarding Detection (S-BFD) provides a simplified mechanism for continuity testing and validation of forwarding paths. Unlike traditional BFD, S-BFD does not require session establishment or negotiation - instead, it uses a reflector model where one side (the initiator) can immediately begin sending BFD packets to the other side (the reflector) without coordinated session state.

https://datatracker.ietf.org/doc/rfc7880/

This PR introduces two new bfd session types to represent the initiator and reflector modes for S-BFD:

typedef enum _sai_bfd_session_type_t
{
    ...
    /** S-BFD Reflector */
    SAI_BFD_SESSION_TYPE_REFLECTOR,

    /** S-BFD Initiator */
    SAI_BFD_SESSION_TYPE_INITIATOR,

} sai_bfd_session_type_t;

The reflector is a simplified mode which can respond to many initiators, so some attributes which would otherwise be mandatory for BFD sessions, are not applicable for S-BFD reflectors. The reflector merely swaps several fields like the SIP<->DIP as documented in the RFC to "reflect" the packet back to the initiator.

The initiator deals with both the origination and monitoring of the BFD packets.

[tjchadaga]

/azp run

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