HTTP internals: consider SSL sockets with pending encryption as usable

We do not decide which socket a HTTP request is sent on until the
socket is actually ready for sending a request (i.e. it is connected
for HTTP requests and encryption is done for HTTPS requests).

When deciding how many sockets we need for the queued requests, we
consider an in-flight socket as free if it is still connecting.
However, we considered a socket that was connected but needed to
complete encryption as busy, and would instead open another socket.
Now, we consider an encrypting socket as in-flight as well.

Change-Id: I93d6743da6fc430d1424c6965e1475865fd97243
Reviewed-by: Richard J. Moore <rich@kde.org>