UPSTREAM: selftests/seccomp: Handle EINVAL on unshare(CLONE_NEWPID)

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.

Change-Id: I8b0d4c8fbbd39f89dcf07c0e5f0afae47c47a17f
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>
(cherry picked from commit ecaaa55c)
Signed-off-by: Edward Liaw <edliaw@google.com>