Problem
-------

Various network drivers are inconsistent in their handling of logging of
link messages.  One of the more annoying things that some drivers do is
flood the logs with link down messages (usually once every 10sec or so) when
trying to transmit packets out the link.

Further, the detailed contents for link status changes are not consistent
from one driver to another.

Notably, the WIFI drivers generally do not do this.


Solution
--------

We propose to modify GLDv3 so that GLDv3 reports (on the behalf of the driver)
when link state changes by logging a simple message to logs.  This would
only be done when the link _changes_, which could be either due to
administrative action or an external event such as a cable disconnect or
reboot or administrative action the link partner.

For Ethernet media, the message will include the speed and duplex mode, as
follows:

	nge0 link up, 1000Mbps, full duplex

The link lost message will simply take the form

	nge0 link down

For all other media types, the link up message will not include any details,
so that it might look like

	ath0 link up

Obviously "nge0" is for the Nvidia GigE driver, and "ath0" is for the
Atheros WiFi driver.  Other drivers, etc. will get their contents here as
well.  The message will appear to come from "mac", and will be prefixed by
the normal syslog details (date, hostname, message ID, etc.) in the system
logs.

Note that side effect of this is that aggregations will also be reported to
the logs:

	"aggr0 link up"  or "aggr0 link down"

The administrator that wants more detail about the link type, mode, etc. can
use dladm to get this information. 

We will be modifying the full set of the current GLDv3 drivers to remove
any driver-specific logging of link changes.  We can do this now, while
GLDv3 is still an ON-private API.

In the future, we expect that these link messages to migrate from syslog
to FMA or some other similar API.