qemu: Disallow NUMA/network tuning for session mode

qemu: Disallow NUMA/network tuning for session mode

Tuning NUMA or network interface parameters requires root
privileges to manage cgroups. Thus an attempt to set some of these
parameters in session mode on a running domain should be invalid
followed by an error. An example might be memory tuning which raises
an error in such case.

The following behavior in session mode will be present after applying
this patch:

  Tuning  |      SET      |   GET  |
----------|---------------|--------|
NUMA      | shut off only | always |
Memory    |     never     | never  |
Interface |     never     | always |

Resolves https://bugzilla.redhat.com/show_bug.cgi?id=1126762