networkd: fix reporting errors from hostnamed

The return value may be -EINVAL or a positive errno from the dbus
message. Check both ranges, otherwise most errors are silently ignored.
resolved: we don't need the DNS server "source" concept anymore, remove it
sd-network: make socket filter programs static const where possible

(also, fix some whitespace/indentation issues, and avoid "index" as identifier in
order to not clash against libc's "index()" call)
resolved: set LLMNR TCP and UDP TTLs to the values suggested by the RFC
resolved: add more debug logging
resolved: the llmnr destination address check applies to queries, not to responses
resolved: when answer A or AAAA questions, order responses by whether addresses are link-local or not
resolved: never attempt negative caching of SOA records
resolved: only cache answer RRs, never additional or authoritative RRs of responses
resolved: follow more closely the recommend timeouts and TTLs from the LLMNR spec
resolved: don't do llmnr on interfaces lacking multicasting
update TODO
resolved: don't allow adding of ANY class/type RRs to local zones
resolved: don't accept messages with ANY RRs
resolved: respond to ANY queries from our zone
update TODO
resolved: re-add support for getting local domain from DHCP

When the code for generating resolv.conf was moved from networkd to
resolved the DHCP domain name code was dropped.