= #17342 Make 2.4 binary compatible with 2.3

(cherry picked from commit 89af8bdb90)

* remove final identifier in serializers

i* revert/deprecate ProtobufSerializer.ARRAY_OF_BYTE_ARRAY

* adding back compatible empty constructor in serializers

* make FSM.State compatible

* add back ActorPath.ElementRegex

* revert SocketOption changes and add SocketOptionV2
  see a6d3704ef6

* problem filter for ActorSystem and ActorPath

* problem filter for ByteString

* problem filter for deprecated Timeout methods

* BalancingPool companion

* ask

* problem filter for ActorDSL

* event bus

* exclude hasSubscriptions

* exclude some problems in testkit

* boundAddress and addressFromSocketAddress

* Pool nrOfInstances

* PromiseActorRef

* check with 2.3.9

* migration guide note

* explicit exclude of final class problems

akka-actor/src/main/scala/akka/io/TcpConnection.scala

@@ -187,7 +187,7 @@ private[io] abstract class TcpConnection(val tcp: TcpExt, val channel: SocketCha
         // continue anyway
         log.debug("Could not enable TcpNoDelay: {}", e.getMessage)
     }
-    options.foreach(_.afterConnect(channel))
+    options.foreach(_.afterConnect(channel.socket))
 
     commander ! Connected(
       channel.socket.getRemoteSocketAddress.asInstanceOf[InetSocketAddress],