QNetworkConfiguration: add public member bearerTypeFamily()

... to let the user know whether he is on e.g. Wifi, 2G, 3G or 4G.
In most cases, this is what the user wants to know anyhow, while
e.g. BearerEVDO or BearerCDMA2000 go into too much detail.

Task-number: QTBUG-31828
Change-Id: I244a4473feb40e106cbc08e09afdee07d4ecc8d7
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Lorn Potter <lorn.potter@jollamobile.com>