qemu: Use proper agent entering function when freezing filesystems

When doing snapshots, the filesystem freeze function used the agent
entering function that expects the qemud_driver unlocked. This might
cause a deadlock of the qemu driver if the agent does not respond.

The only call path of this function has the qemud_driver locked, so this
patch changes the entering functions to those expecting the driver
locked.
(cherry picked from commit e0316b5e)

src/qemu/qemu_driver.c

@@ -10390,6 +10390,7 @@ qemuDomainSnapshotIsAllowed(virDomainObjPtr vm)
     return true;
 }
 
+/* this function expects the driver lock to be held by the caller */
 static int
 qemuDomainSnapshotFSFreeze(struct qemud_driver *driver,
                            virDomainObjPtr vm) {
@@ -10408,9 +10409,9 @@ qemuDomainSnapshotFSFreeze(struct qemud_driver *driver,
         return -1;
     }
 
-    qemuDomainObjEnterAgent(driver, vm);
+    qemuDomainObjEnterAgentWithDriver(driver, vm);
     freezed = qemuAgentFSFreeze(priv->agent);
-    qemuDomainObjExitAgent(driver, vm);
+    qemuDomainObjExitAgentWithDriver(driver, vm);
 
     return freezed;
 }