audit: Re-work match_ipv6()
audit: Re-work match_ipv6()

This function is part of the IP address access control list
infrastructure and given an IPv6 address and network/prefixlen will
check whether the address falls within the given network.

This worked fine with standard /64 networks but showed some problems
when dealing with prefix lengths that weren't a multiple of 8.

This commit replaces the tcp wrappers based code with code based on the
ngx_ptocidr() & ngx_http_access_inet6() functions from the nginx web
server.

Signed-off-by: Andrew Clayton <02e0a999c50b1f88df7a8f5a04e1b76b35ea6a88@digital-domain.net>

ac000/fcgi_app_core,ac000/fcgi_app_core