Update dnsmasq to v2.86

[DL6ER]

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New FTL features in this version:

• Update to dnsmasq v2.86 (see dnsmasq changelog below for the highlights)
• Support Cisco Umbrella/OpenDNS Device ID & Remote IP (see Cisco Umbrella Remote IP/Device ID support #1096)
• Automatically generated queries (typically DNSSEC DNSKEY and DS) are now included in the Query Log and dashboard.
  They can be suppressed by setting SHOW_DNSSEC=false in /etc/pihole/pihole-FTL.conf

CHANGELOG:

Handle DHCPREBIND requests in the DHCPv6 server code.
Thanks to Aichun Li for spotting this ommision, and the initial patch.

Fix bug which caused dnsmasq to lose track of processes forked to handle TCP DNS connections under heavy load. The code checked that at least one free process table slot was available before listening on TCP sockets, but didn't take into account that more than one TCP connection could arrive, so that check was not sufficient to ensure that there would be slots for all new processes. It compounded this error by silently failing to store the process when it did run out of slots. Even when this bug is triggered, all the right things happen, and answers are still returned. Only under very exceptional circumstances, does the bug manifest itself: see https://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2021q2/014976.html
Thanks to Tijs Van Buggenhout for finding the conditions under which the bug manifests itself, and then working out exactly what was going on.

Major rewrite of the DNS server and domain handling code. This should be largely transparent, but it drastically improves performance and reduces memory foot-print when configuring large numbers domains of the form local=/adserver.com/ or local=/adserver.com/# Lookup times now grow as log-to-base-2 of the number of domains, rather than greater than linearly, as before. The change makes multiple addresses associated with a domain work address=/example.com/1.2.3.4 address=/example.com/5.6.7.8 It also handles multiple upstream servers for a domain better; using the same try/retry alogrithms as non domain-specific servers. This also applies to DNSSEC-generated queries. Finally, some of the oldest and gnarliest code in dnsmasq has had a significant clean-up. It's far from perfect, but it is better.

Revise resource handling for number of concurrent DNS queries. This used to have a global limit, but that has a problem when using different servers for different upstream domains. Queries which are routed by domain to an upstream server which is not responding will build up and trigger the limit, which breaks DNS service for all other domains which could be handled by other servers. The change is to make the limit per server-group, where a server group is the set of servers configured for a particular domain. In the common case, where only default servers are declared, there is no effective change.

Improve efficiency of DNSSEC. The sharing point for DNSSEC RR data used to be when it entered the cache, having been validated. After that queries requiring the KEY or DS records would share the cached values. There is a common case in dual-stack hosts that queries for A and AAAA records for the same domain are made simultaneously. If required keys were not in the cache, this would result in two requests being sent upstream for the same key data (and all the subsequent chain-of-trust queries.) Now we combine these requests and elide the duplicates, resulting in fewer queries upstream and better performance. To keep a better handle on what's going on, the "extra" logging mode has been modified to associate queries and answers for DNSSEC queries in the same way as ordinary queries. The requesting address and port have been removed from DNSSEC logging lines, since this is no longer strictly defined.

Connection track mark based DNS query filtering. Thanks to Etan Kissling for implementing this It extends query filtering support beyond what is currently possible with the --ipset configuration option, by adding support for: 1) Specifying allowlists on a per-client basis, based on their associated Linux connection track mark. 2) Dynamic configuration of allowlists via Ubus. 3) Reporting when a DNS query resolves or is rejected via Ubus. 4) DNS name patterns containing wildcards. Disallowed queries are not forwarded; they are rejected with a REFUSED error code.

[DL6ER]

This PR is superseded by the running beta branch release/v5.9 which contains all commits from here.