build: bugfix: Set package repo URL on release build

For example when building 3.17.1.0b01 for Ubiquiti devices
packages would be found at:
http://downloads.aredn.org/releases/3/17/3.17.1.0b01/ar71xx/generic/packages/

This makes BUILD_SET_VERSION setable only for release builds
and not snapshots or development builds.

Change-Id: Ie6218c5e935c48475ed77023131314a7bef890ef

build/buildsteps/kconfig/099-release_version

@@ -46,3 +46,8 @@ CONFIG_IMAGEOPT=y
 CONFIG_VERSIONOPT=y
 CONFIG_VERSION_NUMBER="$MYBUILDNAME"
 EOF
+
+if [ ! -z "$BUILD_SET_VERSION" ]; then
+  hashedpath=$(echo "$BUILD_SET_VERSION" |awk -F'.' '{print $1"/"$2"/"$0}')
+  echo "CONFIG_VERSION_REPO=\"http://downloads.aredn.org/releases/${hashedpath}/%S/packages\""
+fi