Pull up following revision(s) (requested by bouyer in ticket #33):
sys/arch/xen/xen/if_xennet_xenbus.c: revision 1.59
Allocating a fixed, limited number of buffers for receive and sending them
to the network stack is a bad idea, because if all receive buffers sits
in socket queues, the interface receive stalls by lack of buffers.
Instead, get receive pages from a pool_cache(9). Copying to a mbuf cluser
would work too, but testings shows this has an important performance hit.
This also simplifies locking.
While there, notify the dom0 when we add some receive buffers (older
linux dom0 didn't care, but newer one do).
Problem reported and fix tested by Brian Marcotte on port-xen

(riz)