Given how fragile DNS servers are with some DNS types, and given that we really should avoid confusing them with
known-weird lookups, refuse doing lookups for known-obsolete RR types.
If we already degraded the feature level below DO don't bother with sending requests for DS, DNSKEY, RRSIG, NSEC, NSEC3
or NSEC3PARAM RRs. After all, we cannot do DNSSEC validation then anyway, and we better not press a legacy server like
this with such modern concepts.
This also has the benefit that when we try to validate a response we received using DNSSEC, and we detect a limited
server support level while doing so, all further auxiliary DNSSEC queries will fail right-away.
Let's make DNS class helpers more like DNS type helpers, let's move them
from resolved-dns-rr.[ch] into dns-type.[ch].
This also adds two new calls dns_class_is_pseudo() and
dns_class_is_valid_rr() which operate similar to dns_type_is_pseudo()
and dns_type_is_valid_rr() but for classes instead of types.
This should hopefully make handling of DNS classes and DNS types more
alike.
We are unlikely to evert support most of them, but we can at least
display the types properly.
The list is taken from the IANA list.
The table of number->name mappings is converted to a switch
statement. gcc does a nice job of optimizing lookup (when optimization
is enabled).
systemd-resolve-host -t is now case insensitive.
