sdbusplus: use shorter type aliases

The sdbusplus headers provide shortened aliases for many types.
Switch to using them to provide better code clarity and shorter
lines.  Possible replacements are for:
  * bus_t
  * exception_t
  * manager_t
  * match_t
  * message_t
  * object_t
  * slot_t

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I6a559082fed34ae62b648345ead793436d2d03f6
diff --git a/src/callback.hpp b/src/callback.hpp
index 9b729e4..2ee8282 100644
--- a/src/callback.hpp
+++ b/src/callback.hpp
@@ -48,7 +48,7 @@
      *  @param[in] msg - The sdbusplus signal message
      */
     virtual void operator()(Context /* ctx */,
-                            sdbusplus::message::message& /* msg */){};
+                            sdbusplus::message_t& /* msg */){};
 };
 
 /** @class Conditional