prctl-seccomp-filter-v.test: robustify against unrelated prctl invocations
prctl-seccomp-filter-v.test: robustify against unrelated prctl invocations

* tests/prctl-seccomp-filter-v.test: Filter out PR_GET_* prctl calls.

Reported-by: Steve McIntyre <9ce5770b3bb4b2a1d59be2d97e34379cd192299f@einval.com>

cuviper/strace,Saruta/strace,cuviper/strace,Saruta/strace,cuviper/strace,Saruta/strace,Saruta/strace,Saruta/strace,cuviper/strace,cuviper/strace