MFC r199906:

MFC r199906:

  In case the compression result is the same size as the orignal version,
  the compression was useless as well.  Make sure to not update the data
  and return, else we would waste resources when decompressing.

  This also avoids the copyback() changing data other consumers like
  xform_ipcomp.c would have ignored because of no win and sent out without
  noting that compression was used, resulting in invalid packets at the
  receiver.

git-svn-id: svn://svn.freebsd.org/base/stable/8@200147 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f