QHttpNetworkConnection : Fix the case when we only have one channel

QHttpNetworkConnection : Fix the case when we only have one channel

For the Happy eyeballs implementation we use two channels for the case
where a host lookup gives us both Ipv4 and Ipv6 addresses.
In the case where the Connection is setup to only use one channel
we can not use this solution, so in this case we should use the old
way of connecting with one channel.

Task-number: QTBUG-20981
Change-Id: I6590fb4c67d6a8261cd0e4da8f99cd3603bbb524
Reviewed-on: http://codereview.qt.nokia.com/3524
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Peter Hartmann <peter.hartmann@nokia.com>