Replace deprecated IO::Socket::INET6 with IO::Socket::IP.

When setting KTRACE in the environment, client and server write
ktrace files. This simplifies debugging as system calls can be
inspected with kdump.

The divert-packet socket option IP_DIVERTFL, IPPROTO_DIVERT_RESP,
IPPROTO_DIVERT_INIT feature is gone. Remove the corresponding
tests.

Run divert-packet tests also for IPv6.

Add tests for pf divert-packet. Currently UDP packets are tested
with in and out rules. A single packet, the initial packet or the
response packet are diverted and reinjected.