bnxt_en: Ignore 0 value in autoneg supported speed from firmware.

In some situations, the firmware will return 0 for autoneg supported
speed.  This may happen if the firmware detects no SFP module, for
example.  The driver should ignore this so that we don't end up with
an invalid autoneg setting with nothing advertised.  When SFP module
is inserted, we'll get the updated settings from firmware at that time.

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