RFC: use EM_LEGACY_IRQ in if_lem.c ?

if_lem.c ("lem", one of the e1000 drivers) has 2 possible interrupt modes:
EM_LEGACY_IRQ uses the standard dispatch mechanism, whereas
FAST_INTR has a custom handler that signals a taskqueue to do the job.

I have no idea which actual hardware uses it (all of my Intel 1G
cards use either "em" or "igb"), but "lem" is the driver used in
qemu, and there the EM_LEGACY_IRQ gives approx 10% higher packet
rates than the other.

Any objections if i change the default to EM_LEGACY_IRQ ?

	cheers
	luigi