Include ping6 in all device builds

ping6 is currently only included in debug builds. Include it
everywhere, now that it doesn't need to be setuid any more.

Bug: 9469682
Change-Id: Ia78f6b0e5fc8f7042fb99cdb4a0add426bb56c7e
diff --git a/target/product/base.mk b/target/product/base.mk
index 68fed42..7c077f5 100644
--- a/target/product/base.mk
+++ b/target/product/base.mk
@@ -88,6 +88,7 @@
     netcfg \
     netd \
     ping \
+    ping6 \
     platform.xml \
     pppd \
     pm \