net/mlx5e: Fix wrong private flag usage causing checksum disable

MLX5E_PFLAG_* definitions were changed from bitmask to enumerated
values. However, in mlx5e_open_rq(), the proper API (MLX5E_GET_PFLAG macro)
was not used to read the flag value of MLX5E_PFLAG_RX_NO_CSUM_COMPLETE.
Fixed it.

Fixes: 8ff57c18 ("net/mlx5e: Improve ethtool private-flags code structure")
Signed-off-by: Shay Agroskin <shayag@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>