Enable ADB authentication by default.

Change-Id: I942a2df97ef769549b6f76b7c25241380e8df4f1
diff --git a/config/common.mk b/config/common.mk
index fdefbcb..5fccf65 100644
--- a/config/common.mk
+++ b/config/common.mk
@@ -66,6 +66,9 @@
     ro.com.android.dateformat=MM-dd-yyyy \
     ro.com.android.dataroaming=false
 
+# Enable ADB authentication
+ADDITIONAL_DEFAULT_PROPERTIES += ro.adb.secure=1
+
 # Copy over the changelog to the device
 PRODUCT_COPY_FILES += \
     vendor/cm/CHANGELOG.mkdn:system/etc/CHANGELOG-CM.txt