script/symlink-tree.sh: Fix missing config dir

Apparently symlink-tree has not been used in quite some time as it
fails to symlink the always required config dir

Also, if we pulled from git but .git is missing we get
many error messages on the symlinked tree without this
patch (which symlinks .git, if present)

Signed-off-by: Daniel Dickinson <openwrt@daniel.thecshore.com>