BUG/MINOR: activity: always initialize the profiling variable

It happens it was only set if present in the configuration. It's
harmless anyway but can still cause doubts when comparing logs and
configurations so better correctly initialize it.

This should be backported to 1.9.

src/activity.c

@@ -23,7 +23,7 @@
 
 
 /* bit field of profiling options. Beware, may be modified at runtime! */
-unsigned int profiling;
+unsigned int profiling = 0;
 
 /* One struct per thread containing all collected measurements */
 struct activity activity[MAX_THREADS] __attribute__((aligned(64))) = { };