MFC r228479-228480:

MFC r228479-228480:
r228479:
  BCM5720 performance tweak from Broadcom.
   o Allow multiple outstanding read requests from non-LSO read DMA engine.
   o Allow 4KB burst length reads for non-LSO frames.
   o Enable 512B burst length reads for buffer descriptors.

r228480:
  Destroy DMA tag for jumbo RX buffer in device detach.

git-svn-id: svn://svn.freebsd.org/base/stable/9@229867 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f