reapply patch from jasoni@ for ICMP6_PACKET_TOO_BIG
reapply patch from jasoni@ for ICMP6_PACKET_TOO_BIG

both have been lost, due to diff thinking about reversing those
lines after merge

tested

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars