include/uapi/linux/atm_zatm.h: include linux/time.h

Fixes userspace compile error:

error: field ‘real’ has incomplete type
 struct timeval real;  /* real (wall-clock) time */

Signed-off-by: Mikko Rapeli <mikko.rapeli@iki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>