virnetdevtap: Produce more helpful error message in virNetDevTapCreate()

virnetdevtap: Produce more helpful error message in virNetDevTapCreate()

Since v10.8.0-rc1~133 a different error is reported from
virNetDevTapCreate() when the tap device already exists (and
<interface/> XML specifies managed='no'). But the change covers
only one scenario: if multiqueue was requested in <inteface/> XML
BUT pre-created tap device doesn't have multi_queue flag set. The
opposite scenario: if the device has the multi_queue flag set BUT
no multiqueue was specified in the XML. Until now.

Resolves: https://issues.redhat.com/browse/RHEL-118303
Fixes: f6fb097e11a15e390d989411b2660ead0d1a7c10
Fixes: 465a38154f0cfc31d62c4105770e1f4a9599a611
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>