Implemented analogously to souphttpsrc for compatibility. Proxy
prevents sharing the client between element instances.
Change-Id: I50d676fd55f0e1d7051d8cd7d5922b7be4f0c6e8
Only two uses of unsafely setting the pad functions is left:
- fallbacksrc for overriding the chain function of the proxy pad of a
ghost pad
- threadshare for overriding the pad functions after creationg, which
probably needs some fixing at some point