MFC r232019,232021,232025,232027,232029,232031,232040:

MFC r232019,232021,232025,232027,232029,232031,232040:
r232019:
  Give hardware chance to drain active DMA cycles.

r232021:
  If there are not enough RX buffers, release partially allocated RX
  buffers.

r232025:
  Introduce sf_ifmedia_upd_locked() and have driver reset PHY before
  switching to selected media.  While here, set if_drv_flags before
  switching to selected media.

r232027:
  No need to reprogram hardware RX filter when driver is not running.

r232029:
  Remove taskqueue based MII stat change handler.
  Driver does not need deferred link state change processing.
  While I'm here, do not report current link status if interface is
  not UP.

r232031:
  With r232015, sf(4) gets correct speed/duplex of established link.
  Add more strict speed check in sf_miibus_statchg() and do not touch
  MAC config registers when driver lost a link.

r232040:
  Add check for IFF_DRV_RUNNING flag after serving an interrupt and
  don't give RX path more priority than TX path.
  Also remove infinite loop in interrupt handler and limit number of
  iteration to 32. This change addresses system load fluctuations
  under high network load.

git-svn-id: svn://svn.freebsd.org/base/stable/9@233486 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f