selftests: netconsole: Validate interface selection by MAC address

selftests: netconsole: Validate interface selection by MAC address

Extend the existing netconsole cmdline selftest to also validate that
interface selection can be performed via MAC address.

The test now validates that netconsole works with both interface name
and MAC address, improving test coverage.

Suggested-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Andre Carvalho <asantostc@gmail.com>
Link: https://patch.msgid.link/20250812-netcons-cmdline-selftest-v2-1-8099fb7afa9e@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>