netconsole: selftests: Move netconsole selftests to separate target

netconsole: selftests: Move netconsole selftests to separate target

This patch moves netconsole selftests from drivers/net to its own target
in drivers/net/netconsole.

This change helps saving some resources from CI since tests in
drivers/net automatically run against real hardware which are not used
by netconsole tests as they rely solely on netdevsim.

lib_netcons.sh is kept under drivers/net/lib since it is also used by
bonding selftests. Finally, drivers/net config remains unchanged as
netpoll_basic.py requires netconsole (and does leverage real HW testing).

Reviewed-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Andre Carvalho <asantostc@gmail.com>
Link: https://patch.msgid.link/20260127-netcons-selftest-target-v2-1-f509ab65b3bc@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>