A major update to the ure driver.

This update adds support for:
HW VLAN tagging
HW checksum offload for IPv4 and IPv6
tx and rx aggreegation (for full gige speeds)
multiple transactions

In my testing, I am able to get 900-950Mbps depending upon
TCP or UDP, which is a significant improvement over the previous
91Mbps (~8kint/sec*1500bytes/packet*1packet/int).

Reviewed by: hselasky
MFC after: 2 months
Differential Revision: https://reviews.freebsd.org/D25809