Pass current request to filter in RouterFunction extensions

This commit ensures that the proper request is passed in the
Kotlin RouterFunction extension DSL.

Closes gh-27086

spring-webflux/src/main/kotlin/org/springframework/web/reactive/function/server/RouterFunctionDsl.kt

@@ -653,7 +653,7 @@ class RouterFunctionDsl internal constructor (private val init: RouterFunctionDs
 	fun filter(filterFunction: (ServerRequest, (ServerRequest) -> Mono<ServerResponse>) -> Mono<ServerResponse>) {
 		builder.filter { request, next ->
 			filterFunction(request) {
-				next.handle(request)
+				next.handle(it)
 			}
 		}
 	}