Several tests do not set some ports down as part of their cleanup(),
resulting in IPv6 link-local addresses and associated routes not being
deleted.

These leaks were found using a BPF tool that monitors ASIC resources.

Solve this by setting the ports down at the end of the tests.
Signed-off-by: NAmit Cohen <amcohen@nvidia.com>
Reviewed-by: NPetr Machata <petrm@nvidia.com>
Signed-off-by: NIdo Schimmel <idosch@nvidia.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>