Increase wedge index search initial threshold

If the overhead cost is comparable to the current best rdcost,
skip the corresponding wedge index mode search. This improves the
encoding speed by about 10%. The compression performance loss is
in the range of 0.05% and lower.

STATS_CHANGED

Change-Id: Ifd4f5a569ce08860c5bb45638b86ec91e1983f46
diff --git a/av1/encoder/compound_type.c b/av1/encoder/compound_type.c
index 2adee41..14660ff 100644
--- a/av1/encoder/compound_type.c
+++ b/av1/encoder/compound_type.c
@@ -1369,7 +1369,7 @@
           rs2 += get_interinter_compound_mask_rate(&x->mode_costs, mbmi);
 
           mode_rd = RDCOST(x->rdmult, rs2 + rd_stats->rate, 0);
-          if (mode_rd >= ref_best_rd) continue;
+          if (mode_rd >= ref_best_rd / 2) continue;
 
           if (have_newmv_in_inter_mode(this_mode)) {
             tmp_rate_mv = av1_interinter_compound_motion_search(