rtsp-sdp: add payload type to the sdp framesize attribute
rtsp-sdp: add payload type to the sdp framesize attribute

The sdp framesize attribute is desribed in RFC6064. It is specified
for payloading of H263 and has the following form
a=framesize:<payload type> <width>-<height>. The <width>-<height> part
should be added to the caps in a payloader and the <payload type> should
be added by the rtsp-server.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=725334

barisdemiray/gst-rtsp-server,barisdemiray/gst-rtsp-server,barisdemiray/gst-rtsp-server,surround-io/gst-rtsp-server,surround-io/gst-rtsp-server,thaytan/gst-rtsp-server,thaytan/gst-rtsp-server,surround-io/gst-rtsp-server,thaytan/gst-rtsp-server