message: shorten message type

Create an alias `sdbusplus::message_t` to `sdbusplus::message::message`
to reduce duplication.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ib400b12fe4a412c0c0c3d26a88f3fae46445cfa8
diff --git a/test/bus/match.cpp b/test/bus/match.cpp
index 3fa1647..ee76972 100644
--- a/test/bus/match.cpp
+++ b/test/bus/match.cpp
@@ -50,7 +50,7 @@
 TEST_F(Match, FunctorIs_LambdaTakingMessage)
 {
     bool triggered = false;
-    auto trigger = [&triggered](sdbusplus::message::message& /*m*/) {
+    auto trigger = [&triggered](sdbusplus::message_t& /*m*/) {
         triggered = true;
     };
 
@@ -74,7 +74,7 @@
       public:
         bool triggered = false;
 
-        void callback(sdbusplus::message::message& /*m*/)
+        void callback(sdbusplus::message_t& /*m*/)
         {
             triggered = true;
         }