examples/l3fwd-power: fix handling no Rx queue
examples/l3fwd-power: fix handling no Rx queue

If the number of rx queues is zero, it is meaningless to enable
rx interrupt. This patch fixes it.

Fixes: aee3bc79cc34 ("examples/l3fwd-power: enable one-shot Rx interrupt and polling switch")
Cc: stable@dpdk.org

Signed-off-by: Jingjing Wu <64d28b617c3b4840f5ded1bfa611cba7fadfe5c7@intel.com>

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