OPT RR is initialized from packet's RRs + fixes.

src/knot/nameserver/process_query.c

src/knot/server/server.c

src/libknot/edns.c

src/libknot/edns.h

src/libknot/packet/pkt.c

src/libknot/packet/pkt.h

src/libknot/rrset.c

src/utils/dig/dig_exec.c

tests/fake_server.h

tests/process_answer.c

tests/process_query.c

tests/requestor.c