net/sched: act_police: allow 'continue' action offload

Offloading police with action TC_ACT_UNSPEC was erroneously disabled even
though it was supported by mlx5 matchall offload implementation, which
didn't verify the action type but instead assumed that any single police
action attached to matchall classifier is a 'continue' action. Lack of
action type check made it non-obvious what mlx5 matchall implementation
actually supports and caused implementers and reviewers of referenced
commits to disallow it as a part of improved validation code.

Fixes: b8cd5831 ("net: flow_offload: add tc police action parameters")
Fixes: b50e462b ("net/sched: act_police: Add extack messages for offload failure")
Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Tested-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>