nameserver: modules unification + cleanup

src/knot/nameserver/capture.c

src/knot/nameserver/internet.c

src/knot/nameserver/notify.c

src/knot/nameserver/process_answer.c

src/knot/nameserver/process_answer.h

src/knot/nameserver/process_query.c

src/knot/nameserver/process_query.h

src/libknot/packet/pkt.h