=act #15914 Clarify and correct max-received-message-size

(cherry picked from commit c8c07e7a9f8aa4a9b65a9a75e3eb29ea24a99f1f)

akka-actor/src/main/resources/reference.conf

@@ -603,6 +603,9 @@ akka {
       # The maximum number of bytes delivered by a `Received` message. Before
       # more data is read from the network the connection actor will try to
       # do other work.
+      # The purpose of this setting is to impose a smaller limit than the 
+      # configured receive buffer size. When using value 'unlimited' it will
+      # try to read all from the receive buffer.
       max-received-message-size = unlimited
 
       # Enable fine grained logging of what goes on inside the implementation.

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

@@ -533,7 +533,7 @@ class TcpExt(system: ExtendedActorSystem) extends IO.Extension {
     }
     val ReceivedMessageSizeLimit: Int = getString("max-received-message-size") match {
       case "unlimited" ⇒ Int.MaxValue
-      case x           ⇒ getIntBytes("received-message-size-limit")
+      case x           ⇒ getIntBytes("max-received-message-size")
     }
     val ManagementDispatcher: String = getString("management-dispatcher")
     val FileIODispatcher: String = getString("file-io-dispatcher")