MFC r212157:

MFC r212157:
  Unlike most other controllers, NS DP83815/DP83816 controllers seem
  to pad with 0xFF when it encounter short frames.  According to RFC
  1042 the pad bytes should be 0x00.
  Because manual padding consumes extra CPU cycles, introduce a new
  tunable which controls the padding behavior. Turning this tunable
  on will have driver pad manually but it's disabled by default. Users
  can enable software padding by setting the following tunable to
  non-zero value.

  dev.sis.%d.manual_pad="1"

  PR:	kern/35422 (patch not used)

git-svn-id: svn://svn.freebsd.org/base/stable/8@213626 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f