USB devices on active open flush any pending data
However, this breaks PCIe passive notification (EB header is dropped)

The unnecessary dependency of the input synchronizers on the FSM
state made it hard for quartus to meet timing requirements.

This was causing modelsim to freak out.
It had no effect on hardware because it was a don't care situation.
The new code makes explicit that we don't care about the underflow value.

Long-term, once the TX buffering is fixed, this will not be a problem.
In the meantime, it still needs to work. This re-hack fixes the hack.