[SPARK-19669][HOTFIX][SQL] sessionState access privileges compiled failed in TestSQLContext

## What changes were proposed in this pull request?

In [SPARK-19669](https://github.com/apache/spark/commit/0733a54a4517b82291efed9ac7f7407d9044593c) change the sessionState access privileges from private to public, this lead to the compile failed in TestSQLContext

this pr is a hotfix for this.

## How was this patch tested?
N/A

Author: windpiger <songjun@outlook.com>

Closes #17008 from windpiger/hotfixcompile.