net/mlx5: Add sync reset drop mode support

On sync reset flow, firmware may request a PF, which already
acknowledged the unload event, to move to drop mode. Drop mode means
that this PF will reduce polling frequency, as this PF is not going to
have another active part in the reset, but only reload back after the
reset.

Signed-off-by: Moshe Shemesh <moshe@nvidia.com>
Reviewed-by: Aya Levin <ayal@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>