Merge branch 'netconsole-msgid' into main

Merge branch 'netconsole-msgid' into main

Gustavo Luiz Duarte says:

====================
netconsole: Add support for msgid in sysdata

This patch series introduces a new feature to netconsole which allows
appending a message ID to the userdata dictionary.

If the msgid feature is enabled, the message ID is built from a per-target 32
bit counter that is incremented and appended to every message sent to the target.

Example::
  echo 1 > "/sys/kernel/config/netconsole/cmdline0/userdata/msgid_enabled"
  echo "This is message #1" > /dev/kmsg
  echo "This is message #2" > /dev/kmsg
  13,434,54928466,-;This is message #1
   msgid=1
  13,435,54934019,-;This is message #2
   msgid=2

This feature can be used by the target to detect if messages were dropped or
reordered before reaching the target. This allows system administrators to
assess the reliability of their netconsole pipeline and detect loss of messages
due to network contention or temporary unavailability.

---
Changes in v3:
- Add kdoc documentation for msgcounter.
- Link to v2: https://lore.kernel.org/r/20250612-netconsole-msgid-v2-0-d4c1abc84bac@gmail.com

Changes in v2:
- Use wrapping_assign_add() to avoid warnings in UBSAN and friends.
- Improve documentation to clarify wrapping and distinguish msgid from sequnum.
- Rebase and fix conflict in prepare_extradata().
- Link to v1: https://lore.kernel.org/r/20250611-netconsole-msgid-v1-0-1784a51feb1e@gmail.com
====================

Suggested-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Gustavo Luiz Duarte <gustavold@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>