net/mlx5e: Use non-delayed work for update stats

Convert mlx5e update stats work to a normal work structure, since it is
never used delayed.

Add a helper function to queue update stats work on demand which checks
for some conditions and reduce code duplication to have a better
abstraction.

Fixes: ed56c519 ("net/mlx5e: Update NIC HW stats on demand only")
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>