Avoid unnecessary interface down/up operations upon an MTU change
when it does not affect the rings configuration.

Fixes: 461017cb ("net/mlx5e: Support RX multi-packet WQE (Striding RQ)")
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>