qemu: Disable migration with ivshmem

It was never safe anyway and as such shouldn't have been enabled in the
first place.  Future patches will allow hot-(un)pluging of some ivshmem
devices as a workaround.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>

src/qemu/qemu_migration.c

@@ -2352,6 +2352,12 @@ qemuMigrationIsAllowed(virQEMUDriverPtr driver,
                 return false;
             }
         }
+
+        if (vm->def->nshmems) {
+            virReportError(VIR_ERR_OPERATION_INVALID, "%s",
+                           _("migration with shmem device is not supported"));
+            return false;
+        }
     }
 
     return true;