selftests/seccomp: Handle EINVAL on unshare(CLONE_NEWPID)

selftests/seccomp: Handle EINVAL on unshare(CLONE_NEWPID)

commit ecaaa55c9fa5e8058445a8b891070b12208cdb6d upstream.

unshare(CLONE_NEWPID) can return EINVAL if the kernel does not have the
CONFIG_PID_NS option enabled.

Add a check on these calls to skip the test if we receive EINVAL.

Signed-off-by: Terry Tritton <terry.tritton@linaro.org>
Link: https://lore.kernel.org/r/20240124141357.1243457-2-terry.tritton@linaro.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>