Some of the recent QMP changes require at least 2.8.0, but since the
oldest version we officially package for 6.x is 4.0.0 anyway, checking
for at least 3.0 should not break anyone's setup.
Note that this does not affect machine version checks, only the
installed QEMU binary version.
Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>