hypervisor, vmm: Add dynamic control of logging dirty pages

This patch extends slightly the current live-migration code path with
the ability to dynamically start and stop logging dirty-pages, which
relies on two new methods added to the `hypervisor::vm::Vm` Trait. This
patch also contains a complete implementation of the two new methods
based on `kvm` and placeholders for `mshv` in the `hypervisor` crate.

Fixes: #2858

Signed-off-by: Bo Chen <chen.bo@intel.com>

vmm/src/vm.rs

@@ -2156,6 +2156,10 @@ impl Vm {
         self.memory_manager.lock().unwrap().start_memory_dirty_log()
     }
 
+    pub fn stop_memory_dirty_log(&self) -> std::result::Result<(), MigratableError> {
+        self.memory_manager.lock().unwrap().stop_memory_dirty_log()
+    }
+
     pub fn dirty_memory_range_table(
         &self,
     ) -> std::result::Result<MemoryRangeTable, MigratableError> {