qemu: relax shared memory check for vhostuser daemons

qemu: relax shared memory check for vhostuser daemons

For some vhostuser daemons, we validate that the guest memory is shared
with the host.

With earlier versions of QEMU, it was only possible to mark memory
as shared by defining an explicit NUMA topology.  Later, QEMU exposed
the name of the default memory backend (defaultRAMid) so we can mark
that memory as shared.

Since libvirt commit:
  commit bff2ad5d6b1f25da02802273934d2a519159fec7
    qemu: Relax validation for mem->access if guest has no NUMA
we already check for the case when user requests shared memory,
but QEMU did not expose defaultRAMid.

Drop the duplicit check from vhostuser device validation, to make
it pass on hotplug even after libvirtd restart.

This avoids the need to store the defaultRAMid, since we don't really
need it for anything after the VM has been already started.

https://bugzilla.redhat.com/show_bug.cgi?id=2078693
https://bugzilla.redhat.com/show_bug.cgi?id=2177701

Signed-off-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>