gstpad: Only register debug funcptr once.
gstpad: Only register debug funcptr once.

This makes pad initialization 2 times faster and without any contention
over the debug funcptr global lock.

cfoch/gstreamer,cfoch/gstreamer,StreamUtils/gstreamer,collects/gstreamer,Lachann/gstreamer,lubosz/gstreamer,StreamUtils/gstreamer,ahmedammar/platform_external_gst_gstreamer,surround-io/gstreamer,mparis/gstreamer,StreamUtils/gstreamer,justinjoy/gstreamer,krieger-od/gstreamer,mparis/gstreamer,magcius/gstreamer,lubosz/gstreamer,lubosz/gstreamer,krichter722/gstreamer,ensonic/gstreamer,krichter722/gstreamer,ensonic/gstreamer,ensonic/gstreamer,ylatuya/gstreamer,ahmedammar/platform_external_gst_gstreamer,jpxiong/gstreamer,jpxiong/gstreamer,justinjoy/gstreamer,drothlis/gstreamer,cablelabs/gstreamer,magcius/gstreamer,centricular/gstreamer,ylatuya/gstreamer,mrchapp/gstreamer,jpakkane/gstreamer,mparis/gstreamer,lubosz/gstreamer,Lachann/gstreamer,justinjoy/gstreamer,justinjoy/gstreamer,lubosz/gstreamer,surround-io/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,shelsonjava/gstreamer,jpxiong/gstreamer,drothlis/gstreamer,collects/gstreamer,magcius/gstreamer,krieger-od/gstreamer,shelsonjava/gstreamer,jpakkane/gstreamer,mparis/gstreamer,mrchapp/gstreamer,shelsonjava/gstreamer,ylatuya/gstreamer,cfoch/gstreamer,shelsonjava/gstreamer,collects/gstreamer,mrchapp/gstreamer,surround-io/gstreamer,cablelabs/gstreamer,lovebug356/gstreamer,Lachann/gstreamer,mrchapp/gstreamer,krichter722/gstreamer,jpxiong/gstreamer,centricular/gstreamer,cablelabs/gstreamer,krichter722/gstreamer,ahmedammar/platform_external_gst_gstreamer,ensonic/gstreamer,krieger-od/gstreamer,StreamUtils/gstreamer,cablelabs/gstreamer,lovebug356/gstreamer,centricular/gstreamer,centricular/gstreamer,Distrotech/gstreamer,centricular/gstreamer,Distrotech/gstreamer,jpakkane/gstreamer,lovebug356/gstreamer,ahmedammar/platform_external_gst_gstreamer,Distrotech/gstreamer,krieger-od/gstreamer,mparis/gstreamer,drothlis/gstreamer,jpakkane/gstreamer,justinjoy/gstreamer,drothlis/gstreamer,ahmedammar/platform_external_gst_gstreamer,Lachann/gstreamer,ylatuya/gstreamer,magcius/gstreamer,drothlis/gstreamer,cablelabs/gstreamer,surround-io/gstreamer,mrchapp/gstreamer,jpakkane/gstreamer,ylatuya/gstreamer,cfoch/gstreamer,jpxiong/gstreamer,magcius/gstreamer,lovebug356/gstreamer,shelsonjava/gstreamer,surround-io/gstreamer,Distrotech/gstreamer,collects/gstreamer,lovebug356/gstreamer,cfoch/gstreamer,ensonic/gstreamer,Distrotech/gstreamer,Lachann/gstreamer,collects/gstreamer,krieger-od/gstreamer