olsrd: add missing jshn dependency to olsrd-utils

olsrd: add missing jshn dependency to olsrd-utils

The only file shipped by olsrd-utils is olsrd-neigh.sh, which
sources /usr/share/libubox/jshn.sh on its third line. That file
belongs to the jshn package, which is not pulled in by the
olsrd -> libubus -> libubox dependency chain, so on a minimal image
the utility fails immediately with "not found".

Reported-by: openwrt-ai[bot]
Signed-off-by: Josef Schlehofer <redacted>
Co-authored-by: Claude Fable 5 <redacted>