selftests: netconsole: ensure required log level is set on netcons_basic

selftests: netconsole: ensure required log level is set on netcons_basic

This commit ensures that the required log level is set at the start of
the test iteration.

Part of the cleanup performed at the end of each test iteration resets
the log level (do_cleanup in lib_netcons.sh) to the values defined at the
time test script started. This may cause further test iterations to fail
if the default values are not sufficient.

Signed-off-by: Andre Carvalho <asantostc@gmail.com>
Reviewed-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20251121-netcons-basic-loglevel-v1-1-577f8586159c@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>