[SPARK-20764][ML][PYSPARK] Fix visibility discrepancy with numInstances and degreesOfFreedom in LR and GLR - Python version
[SPARK-20764][ML][PYSPARK] Fix visibility discrepancy with numInstances and degreesOfFreedom in LR and GLR - Python version

## What changes were proposed in this pull request?

SPARK-20097 exposed degreesOfFreedom in LinearRegressionSummary and numInstances in GeneralizedLinearRegressionSummary. Python API should be updated to reflect these changes.

## How was this patch tested?
The existing UT

Author: Peng <peng.meng@intel.com>

Closes #18062 from mpjlu/spark-20764.

(cherry picked from commit cfca01136bd7443c1d9daf8e8e256635eec20ddc)
Signed-off-by: Yanbo Liang <452ae006f36be6c70342f33f64bb6f6eb552689c@gmail.com>

jlopezmalla/spark,apache-spark-on-k8s/spark,jlopezmalla/spark,jlopezmalla/spark,apache-spark-on-k8s/spark,publicRoman/spark,publicRoman/spark,apache-spark-on-k8s/spark,apache-spark-on-k8s/spark,apache-spark-on-k8s/spark,jlopezmalla/spark,publicRoman/spark,jlopezmalla/spark,publicRoman/spark,publicRoman/spark,publicRoman/spark,apache-spark-on-k8s/spark,jlopezmalla/spark,jlopezmalla/spark,apache-spark-on-k8s/spark,publicRoman/spark