selftests: forwarding: Fix spelling mistake "succeded" -> "succeeded"

There are two spelling mistakes in check_fail messages. Fix them.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20210118111902.71096-1-colin.king@canonical.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>