OpTracker: Performance regression
In the latest build there is a significant performance drop
because of calling directly _mark_event() from OpRequest
constructor. The call is now replaced by mark_event()
wrapper where it is checking whether op tracking is enabled or not.
The check is also introduced in the overloaded mark_event() which
was missing earlier.

Signed-off-by: Somnath Roy <somnath.roy@sandisk.com>
FileStore: self referencing is removed for Index
Index is not a smart pointer anymore so there is no
point of maintaining self referencing.

Signed-off-by: Somnath Roy <somnath.roy@sandisk.com>