ofproto-dpif-xlate: Fix the memory leak in netflow.

The memory leak was triggered each time on
creating a netflow and subsequently deleting it.

Signed-off-by: Sha Zhang <zhangsha.zhang@huawei.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

ofproto/ofproto-dpif-xlate.c

@@ -1113,6 +1113,7 @@ xlate_xbridge_remove(struct xlate_cfg *xcfg, struct xbridge *xbridge)
     mbridge_unref(xbridge->mbridge);
     dpif_sflow_unref(xbridge->sflow);
     dpif_ipfix_unref(xbridge->ipfix);
+    netflow_unref(xbridge->netflow);
     stp_unref(xbridge->stp);
     rstp_unref(xbridge->rstp);
     hmap_destroy(&xbridge->xports);