Previously we were always setting SpdyWasUsedAttribute for SPDY/HTTP/2/HTTP/1.1
(true/false) which is confusing. Now if HTTP2AllowedAttribute was set to true on
a request, we set HTTP2WasUsedAttribute. Otherwise, as we did before, we're setting
SpdyWasUsedAttribute.
Change-Id: I0c44cfb5469fef0c12719baa951197ee2accee4a
Reviewed-by: Markus Goetz (Woboq GmbH) <markus@woboq.com>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>