MFC r274434:
  Fix ips_out_nosa errors accounting.

MFC r274454:
  ipsec6_process_packet is called before ip6_output fixes ip6_plen.
  Update ip6_plen before bpf processing to be able see correct value.

MFC r274455:
  We don't return sp pointer, thus NULL assignment isn't needed.
  And reference to sp will be freed at the end.

MFC r274465:
  Remove redundant ip6_plen initialization.

MFC r274466:
  Strip IP header only when we act in tunnel mode.

MFC r274467:
  Count statistics for the specific address family.

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