bnxt_en: Refactor the initialization of the ethtool link settings.

Refactor this logic in bnxt_probe_phy() into a separate function
bnxt_init_ethtool_link_settings().  It used to be that the settable
link settings will never be changed without going through ethtool.
So we only needed to do this once in bnxt_probe_phy().  Now, another
function sharing the port may change it and we may need to re-initialize
the ethtool settings again in run-time.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>