EDNS refactoring v2

Refactored the EDNS even more. The `edns_parameters` structure has been removed, only the OPT RR is used everywhere. Also removed any EDNS-related stuff from the packet functions, except for a getter, but there is one for TSIG as well, so it's not an issue probably. It's also possible to remove it, as it only saves a few characters of code.

Unittests pass, functional tests also.

Please review again.

- find_option returns uint8_t *
- Some constants improved.

- No EDNS processing when server's OPT is not set
- Clearing OPT from packet
- Fixed packet unittest (wrong condition)

Conflicts:
	tests/Makefile.am