You may also want to add:
ln -s /mnt/loc/opt/sbin /opt/sbin
If you choose to install man and man-pages with:
ipkg -t /opt/tmp install man
ipkg -t /opt/tmp install man-pages
then will want to add additional sym links for the /opt/man and /opt/info directories else man won't by default find your man pages (or edit man.conf to point to /mnt/loc/opt/man).