This function takes an IPv6 address represented in numeric form as a
binary string, as returned by INET6_ATON(). It returns 1 if the
argument is a valid IPv4-mapped IPv6 address, 0 otherwise. IPv4-mapped
addresses have the form ::ffff:ipv4_address.
mysql> SELECT IS_IPV4_MAPPED(INET6_ATON('::10.0.5.9'));
mysql> SELECT IS_IPV4_MAPPED(INET6_ATON('::ffff:10.0.5.9'));