MFC r251600:
  Avoid unnecessary controller reinitialization by checking driver
  running state.  fxp(4) requires controller reinitialization for the
  following cases.
   o RX lockup condition on i82557
   o promiscuous mode change
   o multicast filter change
   o WOL configuration
   o TSO/VLAN hardware tagging/checksum offloading configuration
   o MAC reprogramming after speed/duplex/flow-control resolution
   o Any events that result in MAC reprogramming(link UP/DOWN,
     remote link partner's restart of auto-negotiation etc)
   o Microcode loading/unloading
  Apart from above cases which come from hardware limitation, upper
  stack also blindly reinitializes controller whenever an IP address
  is assigned. After r194573, fxp(4) no longer needs to reinitialize
  the controller to program multicast filter after upping the
  interface. So keeping track of driver running state should remove
  all unnecessary controller reinitializations.

  This change will also address endless controller reinitialization
  triggered by dhclient(8).