Fix dpdk/ldradix fib lookup algorithm preference calculation.

The current preference number were copied from IPv4 code,
assuming 500k routes to be the full-view. Adjust with the current
reality (100k full-view).

Reported by: Marek Zarychta <zarychtam at plan-b.pwste.edu.pl>
Approved by: re(gjb)

(cherry picked from commit 8a25d3f6ce34b80fef5fd6a324da724c56ad94ed)