Legacy ixgbe driver update, including:
# Support for X550EM devices.
# Initialization code refactoring.
# ixgbe-specific netmap code moved to ixgbe folder (but not removed from dev/netmap/).
# VF driver full split. Some cleanup can be had due to redundant code, but this split goes inline with the refactoring.
**NOTE: This is to be applied on the 10-STABLE tree (and //not// HEAD). The idea is that many of these changes will be ported to the iflib version of ixgbe. The legacy version residing in HEAD may or may not be updated at a later time. For HEAD, our focus will mainly be on the iflib driver.**