MFC r207851:

MFC r207851:
  Implement TSO and TSO over VLAN. Increase number of allowed
  fragmentation of mbuf chain to 32 from 16 because TSO can send 64KB
  sized packet which in turn requires long list of mbuf chain. Due to
  lack of documentation, I'm not sure whether driver have to pull up
  ethernet/IP/TCP header with options to make controller work but
  driver have to parse TCP header to update pseudo TCP checksum
  anyway. The controller expects pseudo TCP checksum computed by
  upper stack and the checksum should follow the MS NDIS
  specification to make TSO work.

  Tested by:	xclin <xclin <> cs dot nctu dot edu dot tw >

git-svn-id: svn://svn.freebsd.org/base/stable/8@208201 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f