virSecuritySELinuxSetTapFDLabel: Temporarily revert to old behavior

virSecuritySELinuxSetTapFDLabel: Temporarily revert to old behavior

https://bugzilla.redhat.com/show_bug.cgi?id=1141879

A long time ago I've implemented support for so called multiqueue
net.  The idea was to let guest network traffic be processed by
multiple host CPUs and thus increasing performance. However, this
behavior is enabled by QEMU via special ioctl() iterated over the
all tap FDs passed in by libvirt. Unfortunately, SELinux comes in
and disallows the ioctl() call because the /dev/net/tun has label
system_u:object_r:tun_tap_device_t:s0 and 'attach_queue' ioctl()
is not allowed on tun_tap_device_t type. So after discussion with
a SELinux developer we've decided that the FDs passed to the QEMU
should be labelled with svirt_t type and SELinux policy will
allow the ioctl(). Therefore I've made a patch
(cf976d9dcf4e592261b14f03572) that does exactly this. The patch
was fixed then by a4431931393aeb1ac5893f121151fa3df4fde612 and
b635b7a1af0e64754016d758376f382470bc11e7. However, things are not
that easy - even though the API to label FD is called
(fsetfilecon_raw) the underlying file is labelled too! So
effectively we are mangling /dev/net/tun label. Yes, that broke
dozen of other application from openvpn, or boxes, to qemu
running other domains.

The best solution would be if SELinux provides a way to label an
FD only, which could be then labeled when passed to the qemu.
However that's a long path to go and we should fix this
regression AQAP. So I went to talk to the SELinux developer again
and we agreed on temporary solution that:

1) All the three patches are reverted
2) SELinux temporarily allows 'attach_queue' on the
tun_tap_device_t

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>