MFC r342649, r342650

netmap: add suite of unit tests

Import the unit tests from upstream (https://github.com/luigirizzo/netmap
ba02539859d46d33), and make them ready for use with Kyua.
There are currently 38 regression tests, which test the kernel control ABI
exposed by netmap to userspace applications:

1: test for port info get
2-5: tests for basic port registration
6-9: tests for VALE
10-11: tests for getting netmap allocator info
12-15: tests for netmap pipes
16: test on polling mode
17-18: tests on options
19-27: tests for sync-kloop subsystem
28-39: tests for null ports
31-38: tests for the legacy NIOCREGIF registers

Reviewed by: ngie
Sponsored by: Sunny Valley Networks
Differential Revision: https://reviews.freebsd.org/D18490