examples/l3fwd: add loop count for hash multi-lookup
examples/l3fwd: add loop count for hash multi-lookup

New macro to define how many times of hash lookup in one time, and this
makes the code more concise.

Signed-off-by: Jianbo Liu <ad48e27d4475ec2c10ba93ba465af79f05639344@linaro.org>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk