scan_ip6 parses an IPv6 number in RFC1884 ASCII representation
from src and writes the result into ip. It returns the
number of bytes read from src or 0 if the parsing failed.
scan_ip6 accepts upper and lower case hex letters, it understands "::"
compression and partial IPv4 addresses as in "::FFFF:126.96.36.199".
To allow transparent usage of IPv4 in IPv6 applications, scan_ip6 also
understands IPv4 addresses in dotted-decimal notation and will return
an IPv4-mapped IPv6 address (i.e. "127.0.0.1" will be parsed as
Unlike many other IP parsing routines, scan_ip6 does not recognize octal
(like 0188.8.131.52) or hexadecimal numbers (like 0x7f000001)
in the IPv4 part.