Incomplete Support for Unicast Hellos

[zmw12306]

Incomplete Support for Unicast Hellos (RFC 8966 Appendix F Non-Compliance)

It seems the current implementation doesn't support unicast at this moment. In the future, it would be important to support:

1. Missing Unicast Hello Sequence Number Tracking
   Problem: The implementation only tracks a single Hello sequence number per neighbor.
   RFC Requirement: Separate sequence numbers must be maintained for unicast and multicast Hellos.
   Suggested Fix:
   Add unicast_hello_seqno_in and unicast_hello_seqno_out fields to the struct neighbor.

2. Incomplete Hello History Tracking
   Problem: A single reach field is used to track Hello history.
   RFC Requirement: Hello histories must be tracked independently for multicast and unicast Hellos.
   Suggested Fix:
   Add separate mcast_reach and ucast_reach fields in the neighbor structure.

3. Incomplete Timer Handling
   Problem: There is no separate timer for unicast Hellos.
   RFC Requirement: Timer logic must independently handle expiration for each Hello type.
   Suggested Fix:
   Add a ucast_hello_time field and update the Hello timer processing logic accordingly.

[riw777]

Are you going to push a commit to fix it?

[github-actions]

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[frrbot]

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