tests/libalias: Add perfomance test utility

In order to compare upcoming changes for their effectivness, measure
performance by counting opertions and the runtime of each operation
over the time. Accumulate all tests in a single instance, so make it
complicated over the time. If you wait long enough, you will notice
the expiry of old flows.

Reviewed by: kp (earlier version)
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D30379