Periodic messages on NetBSD-9 and -current: xennet0: rx no cluster

[Brian Buhrow <buhrow%nfbcal.org@localhost>]

	Hello.  I'm running a number of NetBSD-9 and -current as of 99.77 amd/64 domu machines on
a couple of different servers with FreeBSD as dom0.  I'm getting the following messages from
the kernel: 
xennet0: rx no cluster
Much of the time, these messages seem harmless, but occasionally, the network locks up on
machines that display this message.

In looking at the source code, I get that this is a pool allocation failure in
if_xennet_xenbus.c, but I don't understand which memory resource it's running out of and if
there is a way to increase that resource.  In general, the domu's in question seem to have
plenty of memory and I don't see a lot of memoory pressure for other tasks on the systems.

	Has anyone else seen these messages on their domu machines and does anyone have ideas on
how to correct the issue?
-thanks
-Brian