MFC r257307:
  Fix regression introduced in r235816.
  r235816 triggered kernel panic or hang after warm boot.
  Don't blindly restore BCE_EMAC_MODE media configuration in
  bce_reset().  If driver is about to shutdown it will invoke
  bce_reset() which in turn results in restoring BCE_EMAC_MODE
  media configuration.  This operation seems to confuse controller
  firmware.