Remove unused socket from QNetworkInterface Unix code

This must be a relic from old code, before I split out the code that
uses getifaddrs from the code that doesn't.

Change-Id: Ia1265da6921c7c7a3dc97315d98fed50b3d2fe1c
Reviewed-by: Richard J. Moore <rich@kde.org>
Reviewed-by: Peter Hartmann <phartmann@blackberry.com>
Reviewed-by: Jonas Gastal <gastal@intel.com>
Avoid one extra if_indextoname per address in QNetworkInterface

Given an IPv6 address associated with a network interface, there's a
fairly high chance (of 100%) that any scope ID found is that of the
interface.

Change-Id: Id7315473f39b68ee4c169207168dc2e60fd7d570
Reviewed-by: Richard J. Moore <rich@kde.org>
Reviewed-by: Peter Hartmann <phartmann@blackberry.com>
Reviewed-by: Jonas Gastal <gastal@intel.com>