Add free_bcc_memory to BPFModule (#2147)

Some users uses `BPFModule` directly instead of C++ / Python API, and
they would like to have similar interface of free BCC `.text` memory

src/cc/bpf_module.cc

@@ -35,6 +35,7 @@
 
 #include "common.h"
 #include "bcc_debug.h"
+#include "bcc_elf.h"
 #include "frontends/b/loader.h"
 #include "frontends/clang/loader.h"
 #include "frontends/clang/b_frontend_action.h"
@@ -141,6 +142,10 @@ BPFModule::~BPFModule() {
   ts_->DeletePrefix(Path({id_}));
 }
 
+int BPFModule::free_bcc_memory() {
+  return bcc_free_memory();
+}
+
 // load an entire c file as a module
 int BPFModule::load_cfile(const string &file, bool in_memory, const char *cflags[], int ncflags) {
   ClangLoader clang_loader(&*ctx_, flags_);

src/cc/bpf_module.h

@@ -83,6 +83,7 @@ class BPFModule {
   BPFModule(unsigned flags, TableStorage *ts = nullptr, bool rw_engine_enabled = true,
             const std::string &maps_ns = "");
   ~BPFModule();
+  int free_bcc_memory();
   int load_b(const std::string &filename, const std::string &proto_filename);
   int load_c(const std::string &filename, const char *cflags[], int ncflags);
   int load_string(const std::string &text, const char *cflags[], int ncflags);