Use unix.Prctl() instead of manually reimplementing it using
unix.RawSyscall. Also use unix.SECCOMP_MODE_FILTER instead of locally
defining it.
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Upstream-commit: 6c9d715a8c64a7c782b8c7b57925e1dc19b29517
Component: engine