Dial EventBase loop time logging up to 11

Summary:
There is no need for EventBase to log every loop iteration on a relatively low VLOG level.
Just move it up to 11 like the other verbose logging in EventBase.cpp

Reviewed By: yfeldblum

Differential Revision: D4642379

fbshipit-source-id: 351636afb186ba94b2447b206d7d1389cbdba110

folly/io/async/EventBase.cpp

@@ -364,7 +364,7 @@ bool EventBase::loopBody(int flags) {
     }
 
     if (enableTimeMeasurement_) {
-      VLOG(5) << "EventBase " << this << " loop time: " <<
+      VLOG(11) << "EventBase " << this << " loop time: " <<
         getTimeDelta(&prev).count();
     }