to ``registered'' sockets -- be treated ``specially'', as suggested
by RFC-2367.
The "special" treatment sys/netipsec now gives such messages is that
we use sbappendaddrchain() to deliver the (single) kernel-generated
message to each registered PF_KEY socket, with an sbprio argument of
SB_PRIO_BESTEFFORT, thus by-passing
For now, we check for registered messages, set a local `sbprio'
argument, and call sbappendaddrchain() (as opposed to sbappendaddr())
if and only if sbprio is non-NULL. As noted, we can rework
key_sendup_mbuf(), and all its callers, to pass the sbprio argument;
pending consensus (and hopeful KAME buy-back).