rtc: Set faster ME search method for speed 4

This CL changes search_method used in speed 4.
search_method SF is set to DIAMOND search for boosted
frames and FAST_DIAMOND search for other frames.

          Instruction Count      BD-Rate Loss(%)
cpu-used    Reduction(%)    avg.psnr    ovr.psnr    ssim
   4         30.747          1.0773      1.0731    1.2023

STATS_CHANGED for --rt, speed=4

Change-Id: Ida26776d760ffe04ae77acde9683e8c61fa61360
diff --git a/av1/encoder/speed_features.c b/av1/encoder/speed_features.c
index 9199b62..2ba334c 100644
--- a/av1/encoder/speed_features.c
+++ b/av1/encoder/speed_features.c
@@ -1308,6 +1308,7 @@
   sf->mv_sf.subpel_iters_per_step = 1;
   sf->mv_sf.use_accurate_subpel_search = USE_2_TAPS;
   sf->mv_sf.subpel_search_method = SUBPEL_TREE_PRUNED;
+  sf->mv_sf.search_method = boosted ? DIAMOND : FAST_DIAMOND;
 
   sf->part_sf.ml_prune_partition = 1;
   sf->part_sf.reuse_prev_rd_results_for_part_ab = 1;