bnxt_en: Use common function to get ethtool supported flags.

bnxt_en: Use common function to get ethtool supported flags.

Orabug: 23221795

The supported bits and advertising bits in ethtool have the same
definitions.  The same is true for the firmware bits.  So use the
common function to handle the conversion for both supported and
advertising bits.

v2: Don't use parentheses on function return.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 4b32cacca28fe8b29bf266feff19b6fc2180402e)
Signed-off-by: Brian Maly <brian.maly@oracle.com>