tools: bpftool: support comments in batch files

Replace '#' by '\0' in commands read from batch files in order to avoid
processing the remaining part of the line, thus allowing users to use
comments in the files.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>