iter27 α-27: populate slice_params.num_entry_point_offsets from VAAPI

BBB HEVC uses WPP (entropy_coding_sync_enabled_flag=1); slice header
contains entry_point_offset_minus1 syntax elements. libva was setting
num_entry_point_offsets=0 with the comment 'iter2 doesn't do tiles',
but WPP uses the same mechanism — rkvdec miscounted the slice header
skip distance and read slice data starting at wrong byte for P/B
frames → frame 2+ decoded with garbage reference data.

iter27 kernel printk diff:
  libva frame 2 sl[8..11]  = 00 00 00 00 (=0)
  kdirect frame 2 sl[8..11] = 16 00 00 00 (=22)

VAAPI exposes VASliceParameterBufferHEVC.num_entry_point_offsets.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/h265.c

@@ -79,6 +79,7 @@
 #include <linux/videodev2.h>
 #include <linux/v4l2-controls.h>
 
+#include "utils.h"
 #include "v4l2.h"
 
 /*
@@ -386,7 +387,21 @@ static void h265_fill_slice_params(VAPictureParameterBufferHEVC *picture,
 	 * buffer. FFmpeg pattern at v4l2_request_hevc.c:190. */
 	slice_params->data_byte_offset = source_offset + slice->slice_data_byte_offset;
 
-	slice_params->num_entry_point_offsets = 0;  /* iter2 doesn't do tiles */
+	/*
+	 * iter27 α-27: populate num_entry_point_offsets from VAAPI.
+	 *
+	 * BBB HEVC uses WPP (entropy_coding_sync_enabled_flag); each CTU row
+	 * after the first creates an entry point. For 720p with 32-pixel
+	 * CTUs that's 22 entry points per slice. Hardcoding 0 made rkvdec
+	 * miscount the slice header skip distance → wrong slice data
+	 * boundary → frame 2+ decoded with garbage reference data.
+	 *
+	 * Comment "iter2 doesn't do tiles" was inaccurate: WPP isn't tiles
+	 * but uses the same entry_point_offsets mechanism.
+	 */
+	slice_params->num_entry_point_offsets = slice->num_entry_point_offsets;
+	request_log("iter27diag: slice %p num_entry_point_offsets=%u\n",
+		    (void *)slice, (unsigned)slice->num_entry_point_offsets);
 	slice_params->nal_unit_type = nal_unit_type;
 	slice_params->nuh_temporal_id_plus1 = nuh_temporal_id_plus1;