selftests/seccomp: validate uretprobe syscall passes through seccomp

The uretprobe syscall is implemented as a performance enhancement on
x86_64 by having the kernel inject a call to it on function exit; User
programs cannot call this system call explicitly.

As such, this syscall is considered a kernel implementation detail and
should not be filtered by seccomp.

Enhance the seccomp bpf test suite to check that uretprobes can be
attached to processes without the killing the process regardless of
seccomp policy.

Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Link: https://lore.kernel.org/r/20250202162921.335813-3-eyal.birger@gmail.com


[kees: Skip archs without __NR_uretprobe]
Signed-off-by: Kees Cook <kees@kernel.org>