Storing IPv4 and IPv6 hosts and networks
First: there is no equivalent of the inet type of PostgreSql in MySQL yet.

You should just use the string type to store all kind of IP addresses.
if you need them all in a certain format, convert them before inserting them into the DB. 

If you need to do calculations with them, as you mentioned INET_ATON() and INET_NTOA() are the needed functions to be used.