Leaner BPF debug logic

[grcevski]

We may need to debug the bpf side of things in the field or for our purposes while developing, so we had a mechanism to set the debug level on the bpf side after loading, plus a few macros to support logging levels.

As recently seen in a GitHub actions platform bug, having unnecessary ifs lying around may be problematic for older kernels.

With this change I'm changing how bpf debug printing works in the following way:

• Enablement of debug printing at bpf time is supported by an ifdef macro
• New bpf2go command builds a debug version of the bpf module to be loaded
• At instrumentation load time, if BPF_DEBUG is set to 1 (or TRUE) while launching, we load the debug version of the bpf program. Otherwise we load the non-debug version which has all print statement stripped out, except those that mean errors in what we are reading.

Based on #50, we need that merged first before we review this.

[grcevski]

Thanks Mario!