mlxcx too naive to the possibility of loan default
mlxcx will loan an entire ring's buffers to MAC if it asks for them and they don't get returned, leading the ring to stall and no longer receive traffic. This is undesirable in e.g. the case where a process with very large socket buffer limits fails to
read() from a socket and uses up the entire ring -- then unrelated traffic on the machine will also be stalled with it.
It should cap the number of buffers it will loan, and start copying to freshly allocated mblks past that point.