[C++] add BPF::enable_usdt(void) and disble_usdt(void) to handle all the USDT at once

[gfx]

It's bothering to write a loop such as:

  for (auto &probe : probes) {
    ret = bpf->attach_usdt(probe);
    if (!ret.ok()) {
      std::cerr << "attach_usdt: " << ret.msg() << std::endl;
      return EXIT_FAILURE;
    }
  }

So I think it makes sense when the BPF.h provides a way to enable/disable all the USDTs at once.

[yonghong-song]

[buildbot, test this please]

[yonghong-song]

This may break other applications. Maybe create a new API attach_usdt_all()?

[gfx]

I don't think these overloadings break the compatibility, but giving new names is absolutely better.

Renamed.

[yonghong-song]

[buildbot, test this please]

[yonghong-song]

LGTM. Thanks!