Rename mii_phy_auto_stop() mii_phy_down().
Introduce mii_down(), use it from nge. Do not indirect it to 19 identical
case's in 19 switchstatements like NetBSD did.
. Make internal service routines static.
. Use a consistent ordering of checks in MII_TICK. Do the work in the
mii_phy_tick() subroutine if appropriate.
. Call mii_phy_update() to trigger the callbacks.
Parag Patel did all of the grunt work, so he gets the credit.
Register definitions and actions inferred from a Linux driver,
so Intel also gets some 'credit'.
