Add comments for two SVC related controls
Add comments for two SVC related controls

VP9E_GET_SVC_LAYER_ID
VP9E_REGISTER_CX_CALLBACK

Change-Id: I92060bde1a4830268c8e07190d4ee4c37bc05334

Distrotech/libvpx,Topopiccione/libvpx,mwgoldsmith/vpx,ShiftMediaProject/libvpx,VTCSecureLLC/libvpx,mbebenita/aom,matanbs/webm.libvpx,felipebetancur/libvpx,kleopatra999/webm.libvpx,abwiz0086/webm.libvpx,shyamalschandra/libvpx,Distrotech/libvpx,mbebenita/aom,mbebenita/aom,goodleixiao/vpx,zofuthan/libvpx,mwgoldsmith/vpx,mwgoldsmith/vpx,abwiz0086/webm.libvpx,shacklettbp/aom,altogother/webm.libvpx,mbebenita/aom,thdav/aom,openpeer/libvpx_new,kleopatra999/webm.libvpx,thdav/aom,GrokImageCompression/aom,luctrudeau/aom,kleopatra999/webm.libvpx,luctrudeau/aom,mwgoldsmith/vpx,luctrudeau/aom,kim42083/webm.libvpx,ittiamvpx/libvpx-1,goodleixiao/vpx,Suvarna1488/webm.libvpx,mwgoldsmith/vpx,jacklicn/webm.libvpx,Maria1099/webm.libvpx,jdm/libvpx,thdav/aom,jdm/libvpx,shareefalis/libvpx,ittiamvpx/libvpx-1,running770/libvpx,mbebenita/aom,lyx2014/libvpx_c,openpeer/libvpx_new,webmproject/libvpx,matanbs/webm.libvpx,ShiftMediaProject/libvpx,ittiamvpx/libvpx-1,shacklettbp/aom,mbebenita/aom,luctrudeau/aom,kim42083/webm.libvpx,kim42083/webm.libvpx,mwgoldsmith/vpx,lyx2014/libvpx_c,shareefalis/libvpx,goodleixiao/vpx,running770/libvpx,shacklettbp/aom,jmvalin/aom,stewnorriss/libvpx,ShiftMediaProject/libvpx,iniwf/webm.libvpx,pcwalton/libvpx,jdm/libvpx,altogother/webm.libvpx,openpeer/libvpx_new,webmproject/libvpx,pcwalton/libvpx,shacklettbp/aom,matanbs/webm.libvpx,lyx2014/libvpx_c,VTCSecureLLC/libvpx,liqianggao/libvpx,GrokImageCompression/aom,felipebetancur/libvpx,zofuthan/libvpx,jmvalin/aom,shyamalschandra/libvpx,mbebenita/aom,zofuthan/libvpx,zofuthan/libvpx,felipebetancur/libvpx,gshORTON/webm.libvpx,Suvarna1488/webm.libvpx,Suvarna1488/webm.libvpx,luctrudeau/aom,ittiamvpx/libvpx-1,kalli123/webm.libvpx,jacklicn/webm.libvpx,shyamalschandra/libvpx,kim42083/webm.libvpx,Acidburn0zzz/webm.libvpx,Topopiccione/libvpx,shareefalis/libvpx,reimaginemedia/webm.libvpx,zofuthan/libvpx,jdm/libvpx,iniwf/webm.libvpx,jacklicn/webm.libvpx,Acidburn0zzz/webm.libvpx,kalli123/webm.libvpx,mwgoldsmith/libvpx,liqianggao/libvpx,altogother/webm.libvpx,gshORTON/webm.libvpx,GrokImageCompression/aom,thdav/aom,shareefalis/libvpx,shacklettbp/aom,gshORTON/webm.libvpx,felipebetancur/libvpx,mwgoldsmith/libvpx,ittiamvpx/libvpx-1,stewnorriss/libvpx,reimaginemedia/webm.libvpx,VTCSecureLLC/libvpx,lyx2014/libvpx_c,Maria1099/webm.libvpx,Maria1099/webm.libvpx,ShiftMediaProject/libvpx,abwiz0086/webm.libvpx,smarter/aom,openpeer/libvpx_new,mwgoldsmith/libvpx,GrokImageCompression/aom,Topopiccione/libvpx,iniwf/webm.libvpx,lyx2014/libvpx_c,felipebetancur/libvpx,abwiz0086/webm.libvpx,thdav/aom,Distrotech/libvpx,zofuthan/libvpx,ShiftMediaProject/libvpx,Topopiccione/libvpx,lyx2014/libvpx_c,reimaginemedia/webm.libvpx,webmproject/libvpx,gshORTON/webm.libvpx,mwgoldsmith/libvpx,jdm/libvpx,ittiamvpx/libvpx-1,kim42083/webm.libvpx,Distrotech/libvpx,mbebenita/aom,shyamalschandra/libvpx,GrokImageCompression/aom,GrokImageCompression/aom,iniwf/webm.libvpx,stewnorriss/libvpx,matanbs/webm.libvpx,jmvalin/aom,shyamalschandra/libvpx,abwiz0086/webm.libvpx,liqianggao/libvpx,openpeer/libvpx_new,shacklettbp/aom,mbebenita/aom,running770/libvpx,smarter/aom,kalli123/webm.libvpx,altogother/webm.libvpx,stewnorriss/libvpx,goodleixiao/vpx,kalli123/webm.libvpx,Suvarna1488/webm.libvpx,VTCSecureLLC/libvpx,Acidburn0zzz/webm.libvpx,Topopiccione/libvpx,jdm/libvpx,Maria1099/webm.libvpx,jacklicn/webm.libvpx,running770/libvpx,VTCSecureLLC/libvpx,reimaginemedia/webm.libvpx,kalli123/webm.libvpx,jacklicn/webm.libvpx,stewnorriss/libvpx,reimaginemedia/webm.libvpx,liqianggao/libvpx,kalli123/webm.libvpx,iniwf/webm.libvpx,altogother/webm.libvpx,Suvarna1488/webm.libvpx,running770/libvpx,stewnorriss/libvpx,kim42083/webm.libvpx,Topopiccione/libvpx,felipebetancur/libvpx,luctrudeau/aom,jacklicn/webm.libvpx,thdav/aom,mwgoldsmith/libvpx,shyamalschandra/libvpx,pcwalton/libvpx,smarter/aom,Distrotech/libvpx,gshORTON/webm.libvpx,kleopatra999/webm.libvpx,webmproject/libvpx,smarter/aom,shareefalis/libvpx,jmvalin/aom,iniwf/webm.libvpx,Maria1099/webm.libvpx,goodleixiao/vpx,reimaginemedia/webm.libvpx,pcwalton/libvpx,smarter/aom,liqianggao/libvpx,openpeer/libvpx_new,smarter/aom,Acidburn0zzz/webm.libvpx,abwiz0086/webm.libvpx,kleopatra999/webm.libvpx,pcwalton/libvpx,Acidburn0zzz/webm.libvpx,matanbs/webm.libvpx,Maria1099/webm.libvpx,Suvarna1488/webm.libvpx,running770/libvpx,pcwalton/libvpx,kleopatra999/webm.libvpx,liqianggao/libvpx,webmproject/libvpx,gshORTON/webm.libvpx,webmproject/libvpx,Acidburn0zzz/webm.libvpx,Distrotech/libvpx,goodleixiao/vpx,VTCSecureLLC/libvpx,jmvalin/aom,matanbs/webm.libvpx,shareefalis/libvpx,jmvalin/aom,mwgoldsmith/libvpx,altogother/webm.libvpx