net/mlx5e: Fix a race with XSKICOSQ in XSK wakeup flow

Add a missing spinlock around XSKICOSQ usage at the activation stage,
because there is a race between a configuration change and the
application calling sendto().

Fixes: db05815b

 ("net/mlx5e: Add XSK zero-copy support")
Signed-off-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>