Add stat of inject packet and drop packet

src/packet_io/packet_io.h

@@ -34,6 +34,10 @@ struct io_stat
     uint64_t raw_tx_pkts;
     uint64_t raw_tx_bytes;
 
+    // drop packet
+    uint64_t drop_pkts;
+    uint64_t drop_bytes;
+
     // inject packet
     uint64_t inject_pkts;
     uint64_t inject_bytes;