net/mlx5e: Protect hairpin entry flows list with spinlock

To remove dependency on rtnl lock, extend hairpin entry with spinlock and
use it to protect list of flows attached to hairpin entry from concurrent
modifications.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Reviewed-by: Jianbo Liu <jianbol@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>