makefile: add missing header to include_HEADERS
makefile: add missing header to include_HEADERS

Needed for make distcheck

Signed-off-by: Anders Roxell <b4e8e89057bc64bc4f9625a4a821c9ac177a7ed2@linaro.org>
Reviewed-by: Sorin Vultureanu <8013ba55f8675034bc2ab0d6c3a1c9650437ca36@enea.com>

TolikH/ofp,OpenFastPath/ofp,OpenFastPath/ofp,TolikH/ofp,TolikH/ofp,OpenFastPath/ofp,OpenFastPath/ofp