Add initial support for ATA over Ethernet (AoE) protocol

AoE is a protocol used for ethernet-only block storage.  You can create a VLAN for an array of disks, put a couple of ports on a server on that VLAN, and use the disks over an ethernet switch.  Using the protocol doesn't require as much configuration or packet-level overhead as alternatives, and targets can be very inexpensive devices.

The AoE protocol is not supported by upstream dpkt, but these patches add support.  Feedback is encouraged.