When the tunneled (IPv6) traffic had traffic class bits set (but only >=
16) the packet got lost on the receive side.
This happened because the address family check in ovpn_get_af() failed
to mask correctly, so the version check didn't match, causing us to drop
the packet.
While here also extend the existing 6-in-6 test case to trigger this
issue.
PR: 266598
Sponsored by: Rubicon Communications, LLC ("Netgate")
76e1c9c671