docs: Fixed setAllowGeneratedReplies() link to point to Android N API reference.

<ol>

  <li>Use <a href="{@docRoot}preview/features/notification-updates.html#style">{@code Notification.MessagingStyle}</a>.

  </li>

  <li>Call the method

  <a href="{@docRoot}wear/preview/start.html#get_the_preview_reference_documentation">{@code setAllowGeneratedReplies()}</a>

   for the notification action.</li>

  <li>Call the method {@code setAllowGeneratedReplies()} for the notification action.

  For more information, see the downloadable 

  <a href="{@docRoot}preview/setup-sdk.html#docs-dl">API reference</a>.

  </li>

  <li>Ensure that the notification action has a

    <a href="{@docRoot}reference/android/app/RemoteInput.html">{@code RemoteInput}</a>

     (where the responses will reside).