Make IPMI work in the bce driver even when the interface is configured down.  Formerly, IPMI communication was lost whenever the interface was not up.  The reason was that the BCE_EMAC_MODE register was not configured with the correct media settings.  There are two parts to the fix.
Make IPMI work in the bce driver even when the interface is
configured down.  Formerly, IPMI communication was lost whenever the
interface was not up.  The reason was that the BCE_EMAC_MODE
register was not configured with the correct media settings.  There
are two parts to the fix.

First, resetting the chip in bce_reset() causes the BCE_EMAC_MODE
register to be initialized to a default value that does not
necessarily correspond to the actual media settings.  The fix
implemented here is a bit of a hack.  Ideally, at the end of
bce_reset() we would poll the PHY to determine the negotiated media,
and then we would set the BCE_EMAC_MODE register accordingly.  That
is difficult, since the PHY is abstracted behind the MII layer and is
not supposed to be queried directly from the MAC driver.  Instead,
we read the BCE_EMAC_MODE register at the beginning of bce_reset()
and then restore its media bits to their original values before
returning.  If IPMI is up and running, then the link is already
established and the BCE_EMAC_MODE register is already set appropriately
when bce_reset() is called.  If IPMI is not running, no harm is
done by preserving the BCE_EMAC_MODE settings.  The driver will set
the register properly once the interface is configured up and link
is established.

Second, bce_miibus_statchg() is sometimes called when the link is
down.  In that case, the reported media settings are invalid.
Formerly, the driver used them anyway to setup the BCE_EMAC_MODE
register.  We now avoid changing any MAC registers unless link is
active and the reported media settings are valid.

Submitted by:	jdp
Tested by:	jdp
MFC after:	5 days

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