We couldn't specify the rule for filtering tunnel traffic since an
IPv6 support was committed:

• Stop treating ip' and ipv6' as special in `proto' option as they conflict with /etc/protocols.

• Disuse ipv4' in proto' option as it is corresponding to `ipv6'.

• When protocol is specified as numeric, treat it as it is even it is 41 (ipv6).

• Allow zero for protocol as it is valid number of `ip'.

Still, we cannot specify an IPv6 over an IPv4 tunnel like before such
as:

pass ipv6 from any to any

But, now, you can specify it like:

pass ip4 from any to any proto ipv6

PR: kern/89472
Reported by: Ga l Roualland <gael.rouallandatdial.oleane.com>
MFC after: 1 week