flow control support?

[youfulife]

I find if I change the flow control state when I am receiving packets, the driver is not work.
example:
if flow control is on.
I use this command:
ethtool -A xge0 autoneg off rx off tx off

then the driver can't receive packets, I must reload the driver.

This issue can also be appear when I hot plug the cable. If I hot plug the cable when I running rx sample, I must reload the driver.