socket_listen: interrupt a parent if a child exited

When a child exited, SIGCHLD is sent to parent,
if SIGCHLD has handler without SA_RESTART, the current
syscall will be interrupted.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>