Align transaction trace timestamps with wm and sf trace

Transaction trace uses MONOTONIC while the other traces uses BOOTTIME
which includes CPU suspend time.

Fixes: 152329759
Test: Take winscope traces after the CPU has been suspended for a while and check timestamps
Change-Id: I069827b786913de9f52792c1508dff395966bd11
diff --git a/services/surfaceflinger/SurfaceInterceptor.cpp b/services/surfaceflinger/SurfaceInterceptor.cpp
index 5b3cd69..80102bd 100644
--- a/services/surfaceflinger/SurfaceInterceptor.cpp
+++ b/services/surfaceflinger/SurfaceInterceptor.cpp
@@ -194,7 +194,7 @@
 
 Increment* SurfaceInterceptor::createTraceIncrementLocked() {
     Increment* increment(mTrace.add_increment());
-    increment->set_time_stamp(systemTime());
+    increment->set_time_stamp(elapsedRealtimeNano());
     return increment;
 }