tcpdump tcp[tcpflags] in ipv6/ip6

RST packet capture for ipv6 tcp (40+13=53), or use RST+ACK(&20==20):

tcp and ip6[53] & 4 != 0

so the root issue is libpcap https://github.com/the-tcpdump-group/libpcap/issues/600

powershell helper for nat64 ip extraction:

([ipaddress](read-host 'input ipv6')).getaddressbytes()[-4..-1] -join '.'