selftests/seccomp: Set NNP for TSYNC ESRCH flag test

The TSYNC ESRCH flag test will fail for regular users because NNP was
not set yet. Add NNP setting.

Fixes: 51891498 ("seccomp: allow TSYNC and USER_NOTIF together")
Cc: stable@vger.kernel.org
Reviewed-by: Tycho Andersen <tycho@tycho.ws>
Signed-off-by: Kees Cook <keescook@chromium.org>