fix BIO UDP destroy
diff --git a/core/src/main/java/org/apache/mina/transport/bio/BioUdpServer.java b/core/src/main/java/org/apache/mina/transport/bio/BioUdpServer.java
index 6b228d4..532ffff 100644
--- a/core/src/main/java/org/apache/mina/transport/bio/BioUdpServer.java
+++ b/core/src/main/java/org/apache/mina/transport/bio/BioUdpServer.java
@@ -215,6 +215,6 @@
 
     /** remove a closed session from the list on managed sessions */
     void destroy(BioUdpSession bioUdpSession) {
-        sessions.remove(bioUdpSession);
+        sessions.remove(bioUdpSession.getRemoteAddress());
     }
 }
\ No newline at end of file