To run /usr/sbin/susefirewall2-to-firewalld I have to comment out lines
relative to ip6tables :
ligne 1924 :  
"#     echo "IP_VERSION=ipv6"; ip6tables -w -t mangle -S; ip6tables -w -S;
ip6tables -w -t nat -S \"

ligne 792-794 :
#         if [[ ${tool} == ip*tables ]] && ! ${tool} -w -L > /dev/null 2>&1;
then
#             error "${tool} -w is not usable. ${tool} >= 1.4.20 is needed"
#         fi


The optional Kernel Command Line Parameter is configured like this :
resume=/dev/disk/by-label/LNX_SWAP showopts elevator=deadline ipv6.disable=1

Current iptables is 1.6.2-lp150.1.1

Error message is stupid for leap 15.0 : error ip6tables -w is not usable.
ip6tables >= 1.4.20 is needed