MFC r217247,217381-217382,217384-217385:

MFC r217247,217381-217382,217384-217385:
r217247:
  When driver is not running, do not send DUMP command to controller
  and just show old (cached) values. Controller will not respond to
  the command unless MAC is enabled so DUMP request for down
  interface caused request timeout.

r217381:
  Allow TX/RX checksum offloading to be configured independently.

r217382:
  re_reset() should be called only after setting device specific
  features.

r217384:
  Make sure to check validity of dma maps before destroying.

r217385:
  If driver is not able to allocate RX buffer, do not start driver.
  While I'm here move RX buffer allocation and descriptor
  initialization up to not touch hardware registers in case of RX
  buffer allocation failure.

git-svn-id: svn://svn.freebsd.org/base/stable/8@218899 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f