Commit db7b8eb0 ("add a BPFModule API to disable rw_engine
sscanf/snprintf functions") permits to disable rw_engine so that
memory can be saved for structures with large arrays. As a result,
the function BPFModule::annotate(), which is used to generate
"sscanf" module, is not called when rw_engine is disabled.

Besides generating "sscanf" module, however, BPFModule::annotate()
also sets up several other data structures which are used for
map/table manipulation. This patch implements BPFModule::annotate_light(),
which will be called when rw_engine is disabled, to
setup these data structures.
Signed-off-by: Yonghong Song <yhs@fb.com>