[RFC] device types for s390 network devices

The s390 network devices specifies device types which does not match the
reality.

ctc
===

This device is currently specified as ARPHRD_SLIP. If I see it
correctly, SLIP is an IP-only transport. ctc is more, the link level
header contains the ethernet protocoll type, so it is some sort of
pointopoint ethernet (which is sometimes crippled to IPv4-only for
compatiblity reasons).

qeth
====

This device is currently specified as the corresponding real device
type if it is a real adapter, or ARPHRD_ETHER if it is a virtual one.
The virtual device behaves different in different modi:
- "layer2": In this mode, the device behaves like a real layer 2 device.
- "fake_ll": The kernel prepends a faked link level header.
- default: The kernel processes the IP-packages.  This is the most used
  mode, in whom it is impossible to use a standard libpcap as it parses
  the IP-headers as Ethernet. (IBM suggests to patch libpcap, but I
  think that changing the device type to something more matching is the
  correct solution.)

At least the last part needs some fix, but I don't know how to fix if
properly.

Bastian