igc(4): Introduce new driver for the Intel I225 Ethernet controller.
This controller supports 2.5G/1G/100MB/10MB speeds, and allows
tx/rx checksum offload, TSO, LRO, and multi-queue operation.
The driver was derived from code contributed by Intel, and modified
by Netgate to fit into the iflib framework.
Thanks to Mike Karels for testing and feedback on the driver.
Reviewed by: bcr (manpages), kbowling, scottl, erj
MFC after: 1 month
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D30668