net/mlx5e: Move mlx5e_rq struct declaration

Move struct mlx5e_rq and friends to appear after mlx5e_sq declaration in
en.h.

We will need this for next patch to move the mlx5e_sq instance into
mlx5e_rq struct for XDP SQs.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>