WinRT: Warning about keep-alives not working appears when using HTTP

The following warning appears when using HTTP on WinRT:

Could not set KeepAlive value

The warning doesn't print the error, so that's the first thing which should be fixed (use qErrnoWarning).

When investigating this earlier, the problem appeared to be that the socket engine tries to set this value before the socket is in a valid state for this to be set. If that is indeed the case, the engine should store the http keep alive flag and apply it at a later time as needed.