dapl: quick fix for wrong private data size

DAPl expects the private data size to be up to 256 bytes, but
on windows the private data size is limited to 56 bytes.  As
a result, DAPL can access memory beyond the end of what's
allocated.

A more 'correct' fix is being submitted upstream to dapl.  This
is a simpler fix for the Windows 2.2 release only.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>