IPv6 port-selection hash XORs destination with itself: always zero, no load balancing

Summary

M_FEC_INET6 case(:1056-1057): port=(ip6_dst.s6_addr[15]^ip6_dst.s6_addr[15])&mask. Both operands are dst -> XOR always 0 -> all IPv6 flows pin to port 0. MAC and INET branches correctly use src^dst(:1046-1047,:1051-1052). Typo: should be ip6_src^ip6_dst. No security impact, disables IPv6 load balancing. Fix: ip6_src^ip6_dst.