net/mlx5: Fix HW spec violation configuring uplink

Make sure to modify uplink port to follow only if the uplink_follow
capability is set as required by the HW spec. Failure to do so causes
traffic to the uplink representor net device to cease after switching to
switchdev mode.

Fixes: 7d0314b1

 ("net/mlx5e: Modify uplink state on interface up/down")
Signed-off-by: Eli Cohen <elic@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>