extract_utils: Set filename_from_src: true for CLASS=ETC targets

Change-Id: I881f6a67d84d8de0a4bef17bf3c9eac049679c38

build/tools/extract_utils.sh

@@ -438,6 +438,7 @@ function write_blueprint_packages() {
             printf '\tname: "%s",\n' "$PKGNAME"
             printf '\towner: "%s",\n' "$VENDOR"
             printf '\tsrc: "%s/etc/%s",\n' "$SRC" "$FILE"
+            printf '\tfilename_from_src: true,\n'
         elif [ "$CLASS" = "EXECUTABLES" ]; then
             if [ "$EXTENSION" = "sh" ]; then
                 printf 'sh_binary {\n'