Fix bug of missing to install simple_tc.py

examples/networking/CMakeLists.txt set $EXAMPLE_PROGRAMS twice. The
second one(tc_perf_event.py) overwirte the first one(simple_tc.py).
Signed-off-by: Zhiyi Sun <zhiyisun@gmail.com>

examples/networking/CMakeLists.txt

 set(EXAMPLE_FILES simulation.py)
 set(EXAMPLE_PROGRAMS simple_tc.py)
-set(EXAMPLE_PROGRAMS tc_perf_event.py)
+set(EXAMPLE_PROGRAMS ${EXAMPLE_PROGRAMS} tc_perf_event.py)
 install(FILES ${EXAMPLE_FILES} DESTINATION share/bcc/examples/networking)
 install(PROGRAMS ${EXAMPLE_PROGRAMS} DESTINATION share/bcc/examples/networking)