BUG-529: imrpove statistics collection

This removes synchronized blocks in statistics gathering, as these are
multi-threaded codepaths and we saw contention here.

(cherry picked from commit f8bb9949367e20475284e0761d6311c7d34350eb)
Signed-off-by: Robert Varga <robert.varga@pantheon.sk>
Signed-off-by: Michal Rehak <mirehak@cisco.com>
Change-Id: I45ae2ce258421c95f1381e451c8db267b9e68cc0