ec_smallmul: Enable experiment by default.

Change-Id: I7b26893e9358378f585a892854812ed0a1888385

configure

diff --git a/configure b/configure
index 282dc3b..2619808 100755
--- a/configure
+++ b/configure
@@ -492,6 +492,7 @@
     soft_enable warped_motion
     soft_enable ext_delta_q
     soft_enable loopfiltering_across_tiles
+    soft_enable ec_smallmul
 
     # Backwards/jenkins compatibility with --enable-aom-highbitdepth
     enabled aom_highbitdepth && enable_feature highbitdepth