gdp: Make debug category static

gdp: Make debug category static

Original commit message from CVS:
* libs/gst/dataprotocol/dataprotocol.c:
(gst_dp_header_from_buffer_any), (gst_dp_packet_from_caps_any),
(gst_dp_crc), (gst_dp_header_payload_length),
(gst_dp_header_payload_type), (gst_dp_packet_from_event),
(gst_dp_packet_from_event_1_0), (gst_dp_buffer_from_header),
(gst_dp_caps_from_packet), (gst_dp_event_from_packet_0_2),
(gst_dp_event_from_packet), (gst_dp_validate_header),
(gst_dp_validate_payload):
Make debug category static
Constify the crc table.
Do some more arg checking in public functions.
Fix some docs and do some small cleanups.
* tests/check/libs/gdp.c: (GST_START_TEST), (gst_dp_suite):
Add some more checks to see if GDP deals with bogus input.