packet_filter bug workaround: Disable JIT on generated code.

Theory is that JIT of packet filter rules is triggering a LuaJIT bug,
possibly related to:

  http://www.freelists.org/post/luajit/0LL-nil
Merge pull request #165 from lukego/packet_filter_nojit

packet_filter bug workaround: Disable JIT on generated code.