[MDC-482] simetbox-openwrt-simet-{ma,lmapd}: fix simet-lmapd service

[MDC-482] simetbox-openwrt-simet-{ma,lmapd}: fix simet-lmapd service

* Move the simet-lmapd [procd] initscript to the simetbox-openwrt-
  simet-lmapd package, so that we don't need to check if lmapd is around.

* We must not block some of the initscript invocations ("enable" for
  example) at *image build time*, and we must ensure there are no
  undesired side-effects in that case.

* default_postinst() and default_prerm() from base-files::/lib/rc.common
  (and/or base-files::/lib/functions.sh) already deal with enable/disable,
  leave it to them.

With these changes, simet-lmapd is correctly enabled and started when
sysupgrading from an image that lacked it.