make changes suggested by Brendan from pull request #11

Updated gstdtcpip.c per Brendan's suggestions - note: indentation, comment style, and other GStreamer preferences were not applied to allow easier viewing of the actual changes reflected for:

(1) "Checking for GST_IS_BUFFER is suspicious. Does something go wrong if you just check if (buf)?"

(2) "> +    if (gfr != GST_FLOW_OK)
> +        GST_LOG_OBJECT(filter, "Failure with flow, ret_val=%d", gfr);
This should probably be at least GST_LOG_WARNING"

(3) "This could be done more efficiently with gst_buffer_new_wrapped:
buf = gst_buffer_new_wrapped(cleartext_data, cleartext_size);"