EDNS: Fixed reading of Extended RCODE.
EDNS: Separated "real" RCODEs from error codes.

Although RFC6895 defines error code space to be common for all
response errors, one of them is defined twice (BADVERS / BADSIG).
Also, only Extended RCODE from OPT RR is interpreted together with
RCODE from Header as one number. All other "RCODEs" are separate
error codes with dedicated fields (in TSIG or TKEY RRs).
EDNS: Modified output of utilities.

- Added helper function to retreive whole Extended RCODE to packet.
- RCODE in printed Header should be the Extended RCODE.
EDNS: Return error response in case of BADVERS.
Merge branch 'master' into edns-fixes
utils: code unification
EDNS: Added missing doxygen + minor fixes.
EDNS: Improved version test
tests-extra: fix typo in edns/version
EDNS: Minor fix in doxygen
Merge branch 'edns-fixes' into 'master'

EDNS fixes

- Fixed interpretation of Extended RCODE (was not joining the normal and extended RCODE fields).
- Modified output of Extended RCODE in utilities.
- If BADVERS is returned, return minimal error response. (No Answer)

See merge request !289