6965072: Need API to create SDP sockets

Reviewed-by: michaelm

jdk/src/share/classes/java/net/ServerSocket.java

@@ -68,6 +68,15 @@ class ServerSocket implements java.io.Closeable {
      */
     private boolean oldImpl = false;
 
+    /**
+     * Package-private constructor to create a ServerSocket associated with
+     * the given SocketImpl.
+     */
+    ServerSocket(SocketImpl impl) {
+        this.impl = impl;
+        impl.setServerSocket(this);
+    }
+
     /**
      * Creates an unbound server socket.
      *