simetbox-openwrt-base: work around circular dependencies

simetbox-openwrt-base: work around circular dependencies

* Do not depend on openwrt-simetbox-simet-ma.  We have to use a
  top-down scheme, with the higher-level packages depending on
  the more basic ones, or things break
* Since we are forcing busybox config on simetbox-openwrt-base,
  also add md5sum and sha256sum for simet-ma's benefit