Set DMAC when eth-port has NO-ARP set

When No-ARP flag is set to eth-port, we were not setting the dmac field
in the tunnel-nh rewrite string. As a result, the tunnel packets were
getting dropped in host-os.

Modified code to set physical-interface mac as dest-mac.

Change-Id: I7e58ec0d1c94cefa54abea7c9b1a659ee7b0f41b