Description:
Since update to networkmanager-1.36.2-1 or maybe the version before that, I noticed that my system is sending a "flood" of IPv6 MLD Multicast Listener Report packets.
These are normally sent once in a few minutes, maybe even less. Now I see them sent about 2-3 times in a second.
This is stressing switches and routers, on shared media (i.e. WiFi) this just produces unneccesary traffic and on networks without a IGMPv3 aware switch, these packets are being sent as broadcast to the whole network.
It seems, this issue is caused by NetworkManager or at least a setting, NM is doing on the interface.
When I manually setup the interface, I can't observe this behaviour.


Additional info:
* networkmanager-1.36.2-1
* libnma 1.8.34-1
* Kernel 5.16.15-arch1-1 x86_64
* using KDE's networkmanager GUI

Steps to reproduce:
* Have a network with IPv6 and router advertisements being sent (Autonomous IPv6 addressing)
* Configure NetworkManager to use auto-config für IPv6 on your interface (the default)
* Connect to the network
* Listen to the interface with tcpdump, i.e. with tcpdump -i <interface> -nn 'ip6 && dst host ff02::16'
* You'll see something like this, repeated every ~500 msecs:

14:31:12.567592 IP6 (hlim 1, next-header Options (0) payload length: 116) fe80::e342:3715:ba2a:984b > ff02::16: HBH (rtalert: 0x0000) (padn) [icmp6 sum ok] ICMP6, multicast listener report v2, 5 group record(s) [gaddr ff02::1:ff46:d194 to_ex { }] [gaddr ff02::1:ffb8:f8e8 to_ex { }] [gaddr ff02::fb to_ex { }] [gaddr ff02::1:3 to_ex { }] [gaddr ff02::1:ff2a:984b to_ex { }]

* If the connection is not started by NM and instead setup manually with "ip link set up dev <iface>" and setting "sysctl net.ipv6.conf.<iface>.accept_ra=1", IPv6 connection works, but the flooding does not happen.