smb3: add missing worker function for SMB3 change notify

SMB3 change notify is important to allow applications to wait
on directory change events of different types (e.g. adding
and deleting files from others systems). Add worker functions
for this.

Acked-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>