server: object: add 'action::emit_no_signals'

In a future commit we're going to change the behavior of the destructor
to always emit signals when 'action::defer_emit' is chosen so we need a
placeholder enum to clearly indicate that no signals should ever be
emitted.  Add it now, but keep the same behavior as
'action::defer_emit'.

Change-Id: I606c7739041667186f6141548a377adf91ff5518
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/include/sdbusplus/server/object.hpp b/include/sdbusplus/server/object.hpp
index 2e5652a..7672e2e 100644
--- a/include/sdbusplus/server/object.hpp
+++ b/include/sdbusplus/server/object.hpp
@@ -180,6 +180,7 @@
         emit_object_added,
         emit_interface_added,
         defer_emit,
+        emit_no_signals,
     };
 
     /** Construct an 'object' on a bus with a path.