The seccomp_metadata may be already defined in
system ptrace.h header on recent kernels so
include it.

https://github.com/checkpoint-restore/criu/issues/486#event-1628406918Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>