sixtap_predict_test: enable NEON tests

the offending assembly code was deleted in:
08e38f06 VP8 for ARMv8 by using NEON intrinsics 14

the intrinsics currently pass.

fixes issue #725

Change-Id: I43e4263bef21f9d9008c51ffdfa39fcf10b8e776

test/sixtap_predict_test.cc

@@ -199,7 +199,7 @@ const SixtapPredictFunc sixtap_16x16_neon = vp8_sixtap_predict16x16_neon;
 const SixtapPredictFunc sixtap_8x8_neon = vp8_sixtap_predict8x8_neon;
 const SixtapPredictFunc sixtap_8x4_neon = vp8_sixtap_predict8x4_neon;
 INSTANTIATE_TEST_CASE_P(
-    DISABLED_NEON, SixtapPredictTest, ::testing::Values(
+    NEON, SixtapPredictTest, ::testing::Values(
         make_tuple(16, 16, sixtap_16x16_neon),
         make_tuple(8, 8, sixtap_8x8_neon),
         make_tuple(8, 4, sixtap_8x4_neon)));