ospf6d: CVE-2011-3323 (fortify packet reception)

ospf6d: CVE-2011-3323 (fortify packet reception)

This vulnerability (CERT-FI #514840) was reported by CROSS project.

ospf6d processes IPv6 prefix structures in incoming packets without
verifying that the declared prefix length is valid. This leads to a
crash
caused by out of bounds memory access.

* ospf6_abr.h: new macros for size/alignment validation
* ospf6_asbr.h: idem
* ospf6_intra.h: idem
* ospf6_lsa.h: idem
* ospf6_message.h: idem
* ospf6_proto.h: idem
* ospf6_message.c
  * ospf6_packet_minlen: helper array for ospf6_packet_examin()
  * ospf6_lsa_minlen: helper array for ospf6_lsa_examin()
  * ospf6_hello_recv(): do not call ospf6_header_examin(), let upper
    layer verify the input data
  * ospf6_dbdesc_recv(): idem
  * ospf6_lsreq_recv(): idem
  * ospf6_lsupdate_recv(): idem
  * ospf6_lsack_recv(): idem
  * ospf6_prefixes_examin(): new function, implements A.4.1
  * ospf6_lsa_examin(): new function, implements A.4
  * ospf6_lsaseq_examin(): new function, an interface to above
  * ospf6_packet_examin(): new function, implements A.3
  * ospf6_rxpacket_examin(): new function, replaces
    ospf6_header_examin()
  * ospf6_header_examin(): sayonara
  * ospf6_receive(): perform passive interface check earliest possible,
    employ ospf6_rxpacket_examin()