examples/l3fwd: fix LPM IPv6 subnets

examples/l3fwd: fix LPM IPv6 subnets

Any IP within the 2001:200::/48 subnet will match all the routes given
instead of 1 individual route and the application cannot
differentiate between them.
The change in this patch allows the ports to be individually matched using
smaller /64 ranges for each port. These smaller subnet ranges are still
within the 2001:200::/48 subnet range set aside for benchmarking
in RFC5180.
l3fwd will now use 2001:200:0:{0-7}::/64 where 0-7 is the port ID for IPv6.

Fixes: 37afe381bde4 ("examples/l3fwd: use reserved IP addresses")
Cc: stable@dpdk.org
Signed-off-by: Conor Walsh <conor.walsh@intel.com>
Acked-by: Vladimir Medvedkin <vladimir.medvedkin@intel.com>