test: rtpbin_buffer_list: port to GStreamer 1.0

test: rtpbin_buffer_list: port to GStreamer 1.0

Port the rtpbin_buffer_list test to GStreamer 1.0 and re-enable it.

Some other changes include:
  - the check on the caps has been moved from the buffer level to the
    pad level;
  - remove underscore prefix from static functions names, this is not
    idiomatic in C and rarely used in the other tests;
  - the unused header_buffer variable has been removed;
  - check_group() has been renamed to check_packet() because in
    GStreamer 1.0 there is no concept of "group" anymore, the comments
    have also been updated to reflect this.