netmap: add suite of unit tests

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
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D18490