=htp Extract RemoteAddress.Unknown when cannot find client ip (#21289)

* handle unknown client ip

* updated doc

* fixed java dsl test

akka-http-tests/src/test/java/akka/http/javadsl/server/directives/MiscDirectivesTest.java

@@ -72,7 +72,7 @@ public class MiscDirectivesTest extends JUnitRouteTest {
 
     route
       .run(HttpRequest.create())
-      .assertStatusCode(StatusCodes.NOT_FOUND);
+      .assertStatusCode(StatusCodes.OK);
   }
 
   @Test

akka-http-tests/src/test/scala/akka/http/scaladsl/server/directives/MiscDirectivesSpec.scala

@@ -30,6 +30,11 @@ class MiscDirectivesSpec extends RoutingSpec {
         extractClientIP { echoComplete }
       } ~> check { responseAs[String] shouldEqual "1.2.3.4" }
     }
+    "extract unknown when no headers" in {
+      Get() ~> {
+        extractClientIP { echoComplete }
+      } ~> check { responseAs[String] shouldEqual "unknown" }
+    }
   }
 
   "the selectPreferredLanguage directive" should {