fix #1078: add ff_kni_is_runtime_owner to ff_kni_enqueue stat update

ff_kni_init and ff_kni_alloc were updated in f7961b0 to allocate
kni_stat for the runtime owner secondary, but the enqueue error path
still only updated stats for the owner thread (primary).

Author: jfb8856606

lib/ff_dpdk_kni.c

@@ -604,7 +604,7 @@ ff_kni_enqueue(enum FilterReturn filter, uint16_t port_id, struct rte_mbuf *pkt)
     return 0;
 
 error:
-    if (ff_kni_is_owner_thread()) {
+    if (ff_kni_is_owner_thread() || ff_kni_is_runtime_owner()) {
         kni_stat[port_id]->rx_dropped++;
     }
     rte_pktmbuf_free(pkt);