net: netconsole: selftests: Create a new netconsole selftest

net: netconsole: selftests: Create a new netconsole selftest

Adds a selftest that creates two virtual interfaces, assigns one to a
new namespace, and assigns IP addresses to both.

It listens on the destination interface using socat and configures a
dynamic target on netconsole, pointing to the destination IP address.

The test then checks if the message was received properly on the
destination interface.

Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20240822095652.3806208-1-leitao@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>