Add support for IPv6 networks (on Linux clients) (#1459)

* Feat add basic support for IPv6 networks

Newly generated networks automatically generate an IPv6 prefix of size
64 within the ULA address range, devices obtain a randomly generated
address within this prefix.

Currently, this is Linux only and does not yet support all features
(routes currently cause an error).

* Fix firewall configuration for IPv6 networks

* Fix routing configuration for IPv6 networks

* Feat provide info on IPv6 support for specific client to mgmt server

* Feat allow configuration of IPv6 support through API, improve stability

* Feat add IPv6 support to new firewall implementation

* Fix peer list item response not containing IPv6 address

* Fix nftables breaking on IPv6 address change

* Fix build issues for non-linux systems

* Fix intermittent disconnections when IPv6 is enabled

* Fix test issues and make some minor revisions

* Fix some more testing issues

* Fix more CI issues due to IPv6

* Fix more testing issues

* Add inheritance of IPv6 enablement status from groups

* Fix IPv6 events not having associated messages

* Address first review comments regarding IPv6 support

* Fix IPv6 table being created even when IPv6 is disabled

Also improved stability of IPv6 route and firewall handling on client side

* Fix IPv6 routes not being removed

* Fix DNS IPv6 issues, limit IPv6 nameservers to IPv6 peers

* Improve code for IPv6 DNS server selection, add AAAA custom records

* Ensure IPv6 routes can only exist for IPv6 routing peers

* Fix IPv6 network generation randomness

* Fix a bunch of compilation issues and test failures

* Replace method calls that are unavailable in Go 1.21

* Fix nil dereference in cleanUpDefaultForwardRules6

* Fix nil pointer dereference when persisting IPv6 network in sqlite

* Clean up of client-side code changes for IPv6

* Fix nil dereference in rule mangling and compilation issues

* Add a bunch of client-side test cases for IPv6

* Fix IPv6 tests running on unsupported environments

* Fix import cycle in tests

* Add missing method SupportsIPv6() for windows

* Require IPv6 default route for IPv6 tests

* Fix panics in routemanager tests on non-linux

* Fix some more route manager tests concerning IPv6

* Add some final client-side tests

* Add IPv6 tests for management code, small fixes

* Fix linting issues

* Fix small test suite issues

* Fix linter issues and builds on macOS and Windows again

* fix builds for iOS because of IPv6 breakage

management/server/activity/codes.go

@@ -139,6 +139,14 @@ const (
 	PostureCheckUpdated Activity = 61
 	// PostureCheckDeleted indicates that the user deleted a posture check
 	PostureCheckDeleted Activity = 62
+	// PeerIPv6Enabled indicates that a user enabled IPv6 for a peer
+	PeerIPv6Enabled Activity = 63
+	// PeerIPv6Disabled indicates that a user disabled IPv6 for a peer
+	PeerIPv6Disabled Activity = 64
+	// PeerIPv6InheritEnabled indicates that IPv6 was enabled for a peer due to a change in group memberships.
+	PeerIPv6InheritEnabled Activity = 65
+	// PeerIPv6InheritDisabled indicates that IPv6 was disabled for a peer due to a change in group memberships.
+	PeerIPv6InheritDisabled Activity = 66
 )
 
 var activityMap = map[Activity]Code{
@@ -205,6 +213,10 @@ var activityMap = map[Activity]Code{
 	PostureCheckCreated:                       {"Posture check created", "posture.check.created"},
 	PostureCheckUpdated:                       {"Posture check updated", "posture.check.updated"},
 	PostureCheckDeleted:                       {"Posture check deleted", "posture.check.deleted"},
+	PeerIPv6Enabled:                           {"Peer IPv6 enabled by user", "peer.ipv6.manual_enable"},
+	PeerIPv6Disabled:                          {"Peer IPv6 disabled by user", "peer.ipv6.manual_disable"},
+	PeerIPv6InheritDisabled:                   {"Peer IPv6 disabled due to change in group settings or membership", "peer.ipv6.inherit_disable"},
+	PeerIPv6InheritEnabled:                    {"Peer IPv6 enabled due to change in group settings or membership", "peer.ipv6.inherit_enable"},
 }
 
 // StringCode returns a string code of the activity