cc: define load_func and unload_func public (#1065)

With the current API it is not possible to load any kind of ebpf
program, for example BPF_PROG_TYPE_SCHED_CLS, this commit solves that by
defining load_func and unload_func as part of the public API.
Signed-off-by: Mauricio Vasquez B <mauricio.vasquez@polito.it>

src/cc/BPF.h

@@ -103,11 +103,11 @@ public:
   StatusTuple close_perf_buffer(const std::string& name);
   void poll_perf_buffer(const std::string& name, int timeout = -1);
 
-private:
   StatusTuple load_func(const std::string& func_name, enum bpf_prog_type type,
                         int& fd);
   StatusTuple unload_func(const std::string& func_name);
 
+private:
   std::string get_kprobe_event(const std::string& kernel_func,
                                bpf_probe_attach_type type);
   std::string get_uprobe_event(const std::string& binary_path, uint64_t offset,