[dsc] Allow multiple bpf_program and append content

[Klaus Darilion]

Hi Anand!


> In practice, most folk will have simple bpf expressions that fit on a
> single line. In our config at the RIPE NCC, we have some longer bpf
> expressions, but our dsc config files are generated by templates, and
> not meant for human consumption. The longer lines are therefore
> irrelevant.


Just one note about long BGF filter as we were recently hit by that and noticed only by accident:

If the BPF filter becomes too long, it does not fit into the kernel and libpcap filters in userspace. This is much slower and caused lots of dropped packets on our servers. We only detected the reason as we once run dsc in forground/debug mode - then a warning is logged to the console on startup.

regards
Klaus