Compile dllib with spark2.3 issue

[Le-Zheng]

[ERROR] /home/joy/workspace/BigDL2.0/fixm1/scala212/BigDL/scala/dllib/src/main/scala/com/intel/analytics/bigdl/dllib/nnframes/NNClassifier.scala:326: 
value active is not a member of object org.apache.spark.sql.SparkSession
[ERROR]   val sc = SparkSession.active.sparkContext
[ERROR]    

Dllib with Spark 2.3 failed when compiling https://github.com/intel-analytics/BigDL/blob/main/scala/dllib/src/main/scala/com/intel/analytics/bigdl/dllib/nnframes/NNClassifier.scala#L326

class XGBClassifier (val xgboostParams: Map[String, Any] = Map()) {
  val sc = SparkSession.active.sparkContext

mvn clean package -DskipTests -Dspark.version=2.3.1 -DSPARK_PLATFORM=SPARK_2.3 -P spark_2.x
@dding3 If we need to compile dllib with spark2.3, is there any solution for this issue?