Fix NioSocketChannel usage in graalvm native-image (#13938)

Motivation:

Using NioSocketChannel is currently broken in graalvm native-image
builds. Trying to use it throws:
java.lang.NoSuchMethodException:
io.netty.channel.socket.nio.NioSocketChannel.<init>()

Modification:
Add it to the graalvm metadata json

Result:
Graalvm will include this method as reachable via reflection.

transport/src/main/resources/META-INF/native-image/io.netty/netty-transport/reflect-config.json

@@ -5,6 +5,12 @@
         { "name": "<init>", "parameterTypes": [] }
       ]
     },
+    {
+      "name": "io.netty.channel.socket.nio.NioSocketChannel",
+      "methods": [
+        { "name": "<init>", "parameterTypes": [] }
+      ]
+    },
     {
       "name": "sun.nio.ch.SelectorImpl",
       "fields": [