fixes in nd6_ns_input() for robustness   - do not 'goto bad' unless taddr6 is propery set.   - adjust the pointer to ip6_hdr after IP6_EXTHDR_{GET, CHECK} for safety   - goto bad if check for hoplimit fails
fixes in nd6_ns_input() for robustness
  - do not 'goto bad' unless taddr6 is propery set.
  - adjust the pointer to ip6_hdr after IP6_EXTHDR_{GET, CHECK} for safety
  - goto bad if check for hoplimit fails

MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame