Non-MII card link detection

[Dan Williams <dcbw redhat com>]

Hi,

Ok, so I did non-MII link detection as follows:

Every wired device has a timout function running in the device thread, that
every 2s checks the numbers in:

/sys/class/net/<dev>/statistics/rx_packets
/sys/class/net/<dev>/statistics/collisions

If the numbers have changed within the last 10s, then the code sets link status
to TRUE.  If they have not changed, it sets link status to FALSE.

While this works great at the office, where there are a lot of broadcast packets
around, this works badly for my home network with 1 server and just the laptop,
using a Belkin F5D5020 that doesn't support either MII or ethtool.  There just
isn't enough traffic to update the statistics within 10s necessarily.

So I'm not quite sure what to do... NetworkManager doesn't work really well with
non-carrier-detecting cards right now.  About the only way we can figure out
whether or not the card has carrier-detection is to check both MII ioctl()s and
ethtool ioctl()s.  Even then, we're not necessarily sure it doesn't support
carrier detection, but it'll have to do.

If we don't support carrier detection, we have a few options:

1) Figure out some improvement or other algorithm for the traffic-checking
method.  I've looked at broadcast pings, but that wouldn't endear us to network
administrators at all.  I don't know of another method to force devices to talk
to us.

2) Just disable non-carrier-detect devices from automatic device selection.
They will still appear in the menu and can be used by the user, but they will
never be switched to automatically.

I think at the moment, #2 is probably the best option unless we can come up with
some better version of #1 for these devices.

Dan