bnxt_en: Enhance autoneg support.

On some dual port NICs, the speed setting on one port can affect the
available speed on the other port.  Add logic to detect these changes
and adjust the advertised speed settings when necessary.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>