gst/udp/: Avoid leaking internally allocated file descriptors when setting custom file descriptors. Fixes #543101.

Original commit message from CVS:
Patch by: Peter Kjellerstedt <pkj at axis com>
* gst/udp/gstdynudpsink.c: (gst_dynudpsink_init),
(gst_dynudpsink_finalize), (gst_dynudpsink_set_property),
(gst_dynudpsink_init_send), (gst_dynudpsink_close):
* gst/udp/gstmultiudpsink.c: (gst_multiudpsink_init),
(gst_multiudpsink_finalize), (gst_multiudpsink_set_property):
* gst/udp/gstudpsrc.c: (gst_udpsrc_finalize),
(gst_udpsrc_set_property):
Avoid leaking internally allocated file descriptors when setting
custom file descriptors. Fixes #543101.