core/bpf: prefix log messages from different bpf subsystems
    
    When something goes awry, we would get identical log messages from all the
    bpf subsystems. E.g. "Failed to load BPF object: %m" appeared 5 times in the
    sources. But it is very important to know *which* object we failed to load.
    This could be guessed, e.g. from surroudning messages or from filename/line
    metadata, but when we get log messages in bug reports, this might not be
    available. Let's make the messages distinguishable.
    
    While at it, some messages were adjusted a bit. In particular, we shouldn't use
    internal names like BPFProgram which have no meaning outside of the codebase.
    
    (cherry picked from commit b1acbc08e29cf92ebff3d3e726474c9d642f6d32)