[dsc] Allow multiple bpf_program and append content

[Jerry Lundström]

Hi all,

Please share your thought on if this is a good feature/enhancement:

  https://github.com/DNS-OARC/dsc/issues/127

Related to #108, suggestion is to allow for multiple bpf_program and
append content to previous including one space as delimiter.

  bpf_program "udp port 53";
  bpf_program "and (";
  bpf_program "host 192.168.0.1";
  bpf_program "or host 192.168.0.2";
  bpf_program ")";

Cheers,
Jerry