[RFC] changes in struct dn_pkt_tag ?

I just realized that the struct dn_pkt_tag is 232 bytes,
with the majority of space taken by an unused field,
struct _ip6dn_args (192 bytes), which I'd like to remove.

The structure constitutes the body of a PACKET_TAG_DUMMYNET, is
defined in sys/netinet/ipfw/ip_dn_io.c and private to the dummynet
module.  Do I still need to bump __FreeBSD_version if i remove the
unused field from the structure ?

Related to this, struct _ip6dn_args is also an unused part of
struct ip_fw_args, which however is used by other ipfw clients
such as ng_ipfw, so i am a bit reluctant to "fix" that too.

cheers
luigi