bgpd: implement SendHoldTimer

[eqvinox]

As described by https://www.ietf.org/archive/id/draft-spaghetti-idr-bgp-sendholdtimer-04.html

Since this replicates the HoldTime check on the receiver that is already part of the protocol, I do not believe it necessary to wait for IETF progress on this draft. It's just replicating an existing element of the protocol at the other side of the session.

---

This supersedes #8530 (it's also the "alternate suggestion" mentioned in #8530 (comment))

[NetDEF-CI]

Continuous Integration Result: SUCCESSFUL

Continuous Integration Result: SUCCESSFUL

Congratulations, this patch passed basic tests

Tested-by: NetDEF / OpenSourceRouting.org CI System

CI System Testrun URL: https://ci1.netdef.org/browse/FRR-PULLREQ2-5478/

This is a comment from an automated CI system.
For questions and feedback in regards to this CI system, please feel free to email
Martin Winter - mwinter (at) opensourcerouting.org.

Warnings Generated during build:

Checkout code: Successful with additional warnings

Report for bgp_errors.c | 12 issues
===============================================
< WARNING: line over 80 characters
< #187: FILE: /tmp/f1-31676/bgp_errors.c:187:
< WARNING: line over 80 characters
< #188: FILE: /tmp/f1-31676/bgp_errors.c:188:
< WARNING: line over 80 characters
< #199: FILE: /tmp/f1-31676/bgp_errors.c:199:
< WARNING: line over 80 characters
< #491: FILE: /tmp/f1-31676/bgp_errors.c:491:
< WARNING: line over 80 characters
< #492: FILE: /tmp/f1-31676/bgp_errors.c:492:
< WARNING: line over 80 characters
< #493: FILE: /tmp/f1-31676/bgp_errors.c:493:

[NetDEF-CI]

Continuous Integration Result: SUCCESSFUL

Congratulations, this patch passed basic tests

Tested-by: NetDEF / OpenSourceRouting.org CI System

CI System Testrun URL: https://ci1.netdef.org/browse/FRR-PULLREQ2-5479/

This is a comment from an automated CI system.
For questions and feedback in regards to this CI system, please feel free to email
Martin Winter - mwinter (at) opensourcerouting.org.

Warnings Generated during build:

Checkout code: Successful with additional warnings

Report for bgp_errors.c | 12 issues
===============================================
< WARNING: line over 80 characters
< #187: FILE: /tmp/f1-19208/bgp_errors.c:187:
< WARNING: line over 80 characters
< #188: FILE: /tmp/f1-19208/bgp_errors.c:188:
< WARNING: line over 80 characters
< #199: FILE: /tmp/f1-19208/bgp_errors.c:199:
< WARNING: line over 80 characters
< #491: FILE: /tmp/f1-19208/bgp_errors.c:491:
< WARNING: line over 80 characters
< #492: FILE: /tmp/f1-19208/bgp_errors.c:492:
< WARNING: line over 80 characters
< #493: FILE: /tmp/f1-19208/bgp_errors.c:493:

[eqvinox]

Well I'm an idiot and forgot to cover holdtime == 0 ... will fix later today.