selftests: netdevsim: correct expected FEC strings

ethtool CLI has changed its output. Make the test compatible.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20240114224748.1210578-1-kuba@kernel.org


Signed-off-by: Paolo Abeni <pabeni@redhat.com>