[SPARK-16653][ML][OPTIMIZER] update ANN convergence tolerance param default to 1e-6

## What changes were proposed in this pull request?

replace ANN convergence tolerance param default
from 1e-4 to 1e-6

so that it will be the same with other algorithms in MLLib which use LBFGS as optimizer.

## How was this patch tested?

Existing Test.

Author: WeichenXu <WeichenXu123@outlook.com>

Closes #14286 from WeichenXu123/update_ann_tol.