[SPARK-37887][CORE] Fix the check of repl log level

### What changes were proposed in this pull request?

This patch fixes the check of repl's log level. So we can correctly know if the repl class is set with log level or not.

### Why are the changes needed?

Same as the check in `SparkShellLoggingFilter`, `getLevel` cannot be used anymore to check if the log level is set or not for a logger in log4j2.

### Does this PR introduce _any_ user-facing change?

No

### How was this patch tested?

Manual verified locally.

Closes #35198 from viirya/SPARK-37887.

Authored-by: Liang-Chi Hsieh <viirya@gmail.com>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

Author: viirya

core/src/main/scala/org/apache/spark/internal/Logging.scala

@@ -154,7 +154,11 @@ trait Logging {
         // Use the repl's main class to define the default log level when running the shell,
         // overriding the root logger's config if they're different.
         val replLogger = LogManager.getLogger(logName).asInstanceOf[Log4jLogger]
-        val replLevel = Option(replLogger.getLevel()).getOrElse(Level.WARN)
+        val replLevel = if (Logging.loggerWithCustomConfig(replLogger)) {
+          replLogger.getLevel()
+        } else {
+          Level.WARN
+        }
         // Update the consoleAppender threshold to replLevel
         if (replLevel != rootLogger.getLevel()) {
           if (!silent) {
@@ -229,6 +233,17 @@ private[spark] object Logging {
     "org.apache.logging.slf4j.Log4jLoggerFactory".equals(binderClass)
   }
 
+  // Return true if the logger has custom configuration. It depends on:
+  // 1. If the logger isn't attached with root logger config (i.e., with custom configuration), or
+  // 2. the logger level is different to root config level (i.e., it is changed programmatically).
+  //
+  // Note that if a logger is programmatically changed log level but set to same level
+  // as root config level, we cannot tell if it is with custom configuration.
+  private def loggerWithCustomConfig(logger: Log4jLogger): Boolean = {
+    val rootConfig = LogManager.getRootLogger.asInstanceOf[Log4jLogger].get()
+    (logger.get() ne rootConfig) || (logger.getLevel != rootConfig.getLevel())
+  }
+
   /**
    * Return true if log4j2 is initialized by default configuration which has one
    * appender with error level. See `org.apache.logging.log4j.core.config.DefaultConfiguration`.
@@ -267,17 +282,6 @@ private[spark] object Logging {
       }
     }
 
-    // Return true if the logger has custom configuration. It depends on:
-    // 1. If the logger isn't attached with root logger config (i.e., with custom configuration), or
-    // 2. the logger level is different to root config level (i.e., it is changed programmatically).
-    //
-    // Note that if a logger is programmatically changed log level but set to same level
-    // as root config level, we cannot tell if it is with custom configuration.
-    private def loggerWithCustomConfig(logger: Log4jLogger): Boolean = {
-      val rootConfig = LogManager.getRootLogger.asInstanceOf[Log4jLogger].get()
-      (logger.get() ne rootConfig) || (logger.getLevel != rootConfig.getLevel())
-    }
-
     override def getState: LifeCycle.State = status
 
     override def initialize(): Unit = {