[MDC-461] simetbox-openwrt-simet-lmapd: set queue dir explicitly

[MDC-461] simetbox-openwrt-simet-lmapd: set queue dir explicitly

Explicitly document and set the LMAPd queue to be at
/var/spool/lmapd/queue.  This was already the simet-lmapd default, but
it must be in sync with what simetbox-openwrt-simet-ma and simet-ma
itself expects, so it is best to make it explict in the build script.