Please RUMPify tests in sbin/ifconfig

[Rin Okuyama <rokuyama.rk%gmail.com@localhost>]

Hi,

Recently, tests have been added to tests/sbin/ifconfig, that modify
configuration of *real* interfaces on host.

For example, t_repeated_updown literally does up and down *all*
network interfaces on host repeatedly.

This is not what I expect to tests. I think that they should be
converted to RUMP, and moved into tests/net/if, since:

(1) Tests should not do harm to host. Consider if tests for route(8)
modify the routing table of host. Is this acceptable?

(2) They are not tests for ifconfig(8), but for network interfaces.

(3) Our test-runs on some ports, at least evbarm-earmv7hf, hang in
tests/sbin/ifconfig. This is one of our biggest concerns for netbsd-10.

IMO, all tests with idiom ``for i in $(ifconfig -l); do'' should be
done against shmif(4) instead of real interfaces.

Thanks,
rin