tests/libalias: Test LibAliasIn and redirection

Rework the tests to check the correct layer in a single test. Factor
out tests for reuse in other modules. Extend the test suite for
libalias(3) to incoming connections. Test the various types of
redirections.

gettimeofday(3) is almost as expensive as the calls to libalias.
So the call frequency for this call is reduced by a factor of 1000 in
order to neglect it's influence.

Using NAT entries became more realistic: A communication of a random
length of up to 150 packets (10% outgoing, 90% incoming) is applied
for each entry.

Add port forwardings to the performance tests. This will cause random
incoming packets to match the random port forwardings opends beforehand.

After a long test run, a lot of ressouces have been allocated.
Measure the time tot free them.

Reviewed by: kp (partially)
Differential Revision: https://reviews.freebsd.org/D30412
Differential Revision: https://reviews.freebsd.org/D30408
Differential Revision: https://reviews.freebsd.org/D30405
Differential Revision: https://reviews.freebsd.org/D30443

(cherry picked from commit f1462ab0512c1a0e59f03a7a145df2889bed2997)
(cherry picked from commit 755bab6d55e6e2df168f352f3e2fbdea87002ed8)
(cherry picked from commit 6e87898a2c7e99937656a0c12d03333a43a10c5e)
(cherry picked from commit d62e1ecba07b2acee37e019778087f0f55d977d1)
(cherry picked from commit 5434ebd256a08e452dec376c1488abdf7ff02af8)

Fix various bugs:
(cherry picked from commit ccac04cae538a625cbce224e4005360fa85e1b9d)
(cherry picked from commit 7b8696bf128754712a24ba98ce2d88eed2ee68dc)
(cherry picked from commit fef99da69f983566de3cb8ad4a1b8decc31348ce)
(cherry picked from commit f4c460dacdda5c6e1896a0c51d6096c4f3417b32)