e1000e: Tx hang on I218 when linked at 100Half and slow response at 10Mbps

Tx hang is an unintended consequence of another workaround that is in the
EEPROM for an issue with the firmware at 10Mbps when K1 (a power mode of
the MAC-PHY interconnect) is enabled.  The issue is resolved by setting
appropriate Tx re-transmission timeouts in the PHY and associated K1 entry
times in the MAC to allow enough transmissions to occur without triggering
a Tx hang.  A similar change is needed when linked at 10Mbps to improve
latency.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>