examples/l3fwd: make destination mac address configurable
examples/l3fwd: make destination mac address configurable

Add a command-line parameter to l3fwd, to allow the user to specify the
destination mac address for each ethernet port used.

Signed-off-by: Andrey Chilikin <e7d64155883734f893a62d2f3554768227530801@intel.com>
Signed-off-by: Bruce Richardson <66b9e8e8fbd5e9f41f91b0af050876182ce9d0e4@intel.com>

msune/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,mixja/dpdk,msune/dpdk,venkynv/dpdk-mirror,mixja/dpdk,msune/dpdk,msune/dpdk,venkynv/dpdk-mirror,tsphillips/dpdk-fork,john-mcnamara-intel/dpdk,tsphillips/dpdk-fork,mixja/dpdk,mixja/dpdk,venkynv/dpdk-mirror,john-mcnamara-intel/dpdk,tsphillips/dpdk-fork,venkynv/dpdk-mirror,tsphillips/dpdk-fork