For the four versions of hardware that we (currently) support microcode
download on, the default configuration of our receive interrupt mitigation
microcode was too aggressive, and caused unnecessary delays when pinging,
and low(er) throughput on single connection latency sensitive performance
tests.

This code adds microcode support, and sets the defaults to more reasonable
settings. It also explains the functionality in the code in more detail.
Compile and load tested, shows expected behavior for slight delay of ping
packets (1-2ms) when ucode is loaded, and decent interrupt moderation for
small packets, while maintaining good throughput.
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>