Merge branch 'netconsole-selftest-for-userdata-overflow'

Breno Leitao says:

====================
netconsole: selftest for userdata overflow

Implement comprehensive testing for netconsole userdata entry handling,
demonstrating correct behavior when creating maximum entries and
preventing unauthorized overflow.

Refactor existing test infrastructure to support modular, reusable
helper functions that validate strict entry limit enforcement.

Also, add a warning if update_userdata() sees more than
MAX_USERDATA_ITEMS entries. This shouldn't happen and it is a bug that
shouldn't be silently ignored.

v2: https://lore.kernel.org/20250103-netcons_overflow_test-v2-0-a49f9be64c21@debian.org
v1: https://lore.kernel.org/20241204-netcons_overflow_test-v1-0-a85a8d0ace21@debian.org
====================

Link: https://patch.msgid.link/20250108-netcons_overflow_test-v3-0-3d85eb091bec@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>