swaps and swapl could ref uninit mem in dead trace

a dead trace may still have a non-NULL format_data pointer. e.g. when calling
pcapfile_prepare_packet (by way of trace_prepare_packet), pcapfile_init_input is
called, creating state and associating it with trace->format_data.
add missing trace_destroy_packet in tracestats
replace the extremely slow REQ/REP with PUB/SUB
switch from czmq to low-level zmq api
fix bug where bpf would 'fix' the timestamp twice.

this resulted in a corrupted bpf capture header