QTcpSocket IPv4/6 connect time optimization

Optimize QTcpSocket to minimize connection time when a host name resolves to both an IPv4 and IPv6 address.
One possible route is to perform a two-pass connection attempt, as follows:

• Attempt to connect to the v6 address with a reduced (3 second?) timeout
• If connection attempt #1 times out, attempt to connect to the v4 address with a reduced timeout
• If connection attempt #2 times out, try to connect to the v6 address with the full timeout
• If connection attempt #3 times out, try to connect to the v4 address with the full timeout