Add cdceem(4) driver, for virtual ethernet devices compliant
with Communication Device Class Ethernet Emulation Model (CDC EEM).
The driver supports both the device, and host side operation; there
is a new USB template (#11) for the former.

This enables communication with virtual USB NIC provided by iLO 5,
as found in new HPE Proliant servers.

Reviewed by: hselasky
MFC after: 2 weeks
Relnotes: yes
Sponsored by: Hewlett Packard Enterprise