[XrdSsi] Updates CMakeLists.txt after XRootD SSI change

XrdSsi headers will be merged into master branch, but move into private/

cmdline/CMakeLists.txt

@@ -40,6 +40,6 @@ find_package(xrootd REQUIRED)
 find_package(Protobuf3 REQUIRED)
 find_package(cryptopp REQUIRED)
 
-include_directories(${PROTOBUF3_INCLUDE_DIRS} ${XROOTD_INCLUDE_DIR} ../xroot_ssi_pb)
+include_directories(${PROTOBUF3_INCLUDE_DIRS} ${XROOTD_INCLUDE_DIR} ${XROOTD_INCLUDE_DIR}/private ../xroot_ssi_pb)
 add_executable(eoscta_stub EosCtaStub.cpp)
 target_link_libraries (eoscta_stub cryptopp ctaeosmessages ${PROTOBUF3_LIBRARIES} XrdSsi-4 XrdSsiLib)