memory: call log_start after region_add

It might be confusing for some listener implementations that implement
both, region_add and log_start (e.g. KVM) if we call log_start before an
actual region was added using region_add.

This makes current KVM code trigger an assertion
("kvm_section_update_flags: error finding slot"). So let's just reverse
the order instead of tolerating log_start on yet unknown regions.

Reported-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20171016144302.24284-2-david@redhat.com>
Tested-by: Joe Clifford <joeclifford@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

memory.c

@@ -2607,12 +2607,12 @@ static void listener_add_address_space(MemoryListener *listener,
             .offset_within_address_space = int128_get64(fr->addr.start),
             .readonly = fr->readonly,
         };
-        if (fr->dirty_log_mask && listener->log_start) {
-            listener->log_start(listener, &section, 0, fr->dirty_log_mask);
-        }
         if (listener->region_add) {
             listener->region_add(listener, &section);
         }
+        if (fr->dirty_log_mask && listener->log_start) {
+            listener->log_start(listener, &section, 0, fr->dirty_log_mask);
+        }
     }
     if (listener->commit) {
         listener->commit(listener);