cifs: Send witness register messages to userspace daemon in echo task

If the daemon starts after mounting a share, or if it crashes, this
provides a mechanism to register again.

Signed-off-by: Samuel Cabrero <scabrero@suse.de>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>