MFC r251995:
  Use ICMP6STAT_INC() macro for ICMPv6 errors accounting.
MFC r252007:
  Use RIP6STAT_INC() macro for raw ip6 statistics accounting.
MFC r252009:
  Use PIM6STAT_INC() and MRT6STAT_INC() macros for IPv6 multicast
  statistics accounting.