Resolve ERR_MISSING_GLUE / ERR_EXTRA_AAAA value collision

Resolve ERR_MISSING_GLUE / ERR_EXTRA_AAAA value collision

Both constants were defined as 5. The symbol table used by checkns() to
deduplicate log messages keys on (name, error_code), so logging an
extra-AAAA error caused logged() to also return true for the
missing-glue check, silently skipping the entire missing-glue block for
the same name in named-checkzone and named-checkconf -z.

Convert the ERR_* defines to an auto-numbered enum so the compiler
guarantees the values stay pairwise distinct.

Assisted-by: Claude:claude-opus-4-7
(cherry picked from commit 72d21a08063400d9a3e9c3d13ccc5ac28bf457c1)