astobj2: tweak ao2_replace to do nothing when it would be a NoOp

This change causes ao2_replace to do nothing when src == dst. This
avoids REF_DEBUG logging when we're not actually doing anything.

Review: https://reviewboard.asterisk.org/r/3743/
........

Merged revisions 418396 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@418397 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/astobj2.h

@@ -561,13 +561,15 @@ int __ao2_ref(void *o, int delta);
 	{\
 		typeof(dst) *__dst_ ## __LINE__ = &dst; \
 		typeof(src) __src_ ## __LINE__ = src; \
-		if (__src_ ## __LINE__) {\
-			ao2_ref(__src_ ## __LINE__, +1); \
+		if (__src_ ## __LINE__ != *__dst_ ## __LINE__) { \
+			if (__src_ ## __LINE__) {\
+				ao2_ref(__src_ ## __LINE__, +1); \
+			} \
+			if (*__dst_ ## __LINE__) {\
+				ao2_ref(*__dst_ ## __LINE__, -1); \
+			} \
+			*__dst_ ## __LINE__ = __src_ ## __LINE__; \
 		} \
-		if (*__dst_ ## __LINE__) {\
-			ao2_ref(*__dst_ ## __LINE__, -1); \
-		} \
-		*__dst_ ## __LINE__ = __src_ ## __LINE__; \
 	}
 
 /*! @} */