test/libalias: Tests for instantiation and outgoing NAT

In order to modify libalias for performance, the existing
functionality must not change. Enforce this.

Testing LibAliasOut functionality. This concentrates the typical use
case of initiating data transfers from the inside. Provide a
exhaustive test for the data structure in order to check for
performance improvements.

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
Differential Revision: https://reviews.freebsd.org/D30307
Differential Revision: https://reviews.freebsd.org/D30335
Differential Revision: https://reviews.freebsd.org/D30379

(cherry picked from commit 7fd8baee756efa18b6bbb17cbf3a652eb2058d87)
(cherry picked from commit c1fbb54f4b100d576da7ab065d1887a21f691936)
(cherry picked from commit 33c1bdfc3e098862100bab7a8dc729d8c78ffa7c)