parasite-syscall: print syscall number as %lu

We will still able to distinguish if it's garbage in ax register, but
this is definitely prettier:
(00.036900) 687 was trapped
(00.036903) 687 is going to execute the syscall 158
(00.036928) 687 was trapped
(00.036931) 687 is going to execute the syscall 173

Than that:
(00.024403) 687 was trapped
(00.024407) 687 is going to execute the syscall 9e
(00.024419) 687 was trapped
(00.024421) 687 is going to execute the syscall ad

Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>