FreeBSD 10 network flapping, ix driver unreliable?

[Kevin Bowling]

Hi,

I have FreeBSD 10.0-RELEASE installed on two Dell C6100 nodes.  Each 
node has an Intel X520-DA2 dual port 10gig card.  One of the ports on 
each go to a switch using direct attach coaxial cables.  The other port 
is directly connected between the two nodes (think crossover in twisted 
pair terminology) again using direct attach coaxial cables.

On both machines, and on both ports (including the "crossover"), the 
links flap several times per day.

I've pasted the output of lspci -vv and dmesg here:
https://gist.github.com/kev009/9024442

There's nothing outstanding about the setup otherwise.  I suspected some 
interaction with the switch initially but the "crossover" has eliminated 
that suspicion.

It seems the ix driver is not very reliable under common conditions, 
i.e. https://forums.freebsd.org/viewtopic.php?f=7&t=44570 and a search 
of this list.  Any recommendations or tests?

Regards,
Kevin Bowling