net/mlx5e: Choose best nearest LRO timeout

Instead of predicting the index of the wanted LRO timeout value from
hardware capabilities, look for the nearest LRO timeout value.

Fixes: 5c50368f ('net/mlx5e: Light-weight netdev open/stop')
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Mohamad Haj Yahia <mohamad@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>