selftest: netcons: add test for netconsole over bonded interfaces

selftest: netcons: add test for netconsole over bonded interfaces

This patch adds a selftest that verifies netconsole functionality
over bonded network interfaces using netdevsim. It sets up two bonded
interfaces acting as transmit (TX) and receive (RX) ends, placed in
separate network namespaces. The test sends kernel log messages and
verifies that they are properly received on the bonded RX interfaces
with both IPv4 and IPv6, and using basic and extended netconsole
formats.

This patchset aims to test a long-standing netpoll subsystem where
netpoll has multiple users. (in this case netconsole and bonding). A
similar selftest has been discussed in [1] and [2].

This test also tries to enable bonding and netpoll in different order,
just to guarantee that all the possibilities are exercised.

Link: https://lore.kernel.org/all/20250905-netconsole_torture-v3-0-875c7febd316@debian.org/
Link: https://lore.kernel.org/lkml/96b940137a50e5c387687bb4f57de8b0435a653f.1404857349.git.decot@googlers.com/
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20251107-netconsole_torture-v10-4-749227b55f63@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>