seccomp: fix killing of whole process instead of thread

seccomp: fix killing of whole process instead of thread

Back in 2018 we introduced support for killing the whole QEMU process
instead of just one thread, when a seccomp rule is violated:

  commit bda08a5764d470f101fa38635d30b41179a313e1
  Author: Marc-André Lureau <marcandre.lureau@redhat.com>
  Date:   Wed Aug 22 19:02:48 2018 +0200

    seccomp: prefer SCMP_ACT_KILL_PROCESS if available

Fast forward a year and we introduced a patch to avoid killing the
process for resource control syscalls tickled by Mesa.

  commit 9a1565a03b79d80b236bc7cc2dbce52a2ef3a1b8
  Author: Daniel P. Berrangé <berrange@redhat.com>
  Date:   Wed Mar 13 09:49:03 2019 +0000

    seccomp: don't kill process for resource control syscalls

Unfortunately a logic bug effectively reverted the first commit
mentioned so that we go back to only killing the thread, not the whole
process.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Eduardo Otubo <otubo@redhat.com>