ovs-ofctl: Fix "cookie mask" issue in diff-flows command.

Commit e729e79 (Add ability to restrict flow mods and flow stats
requests to cookies.) introduced a cookie_mask field to the
ofputil_flow_stats_request struct that allowed restricting the flows to
a particular cookie pattern.  The diff-flows command uses the
read_flows_from_switch() function, which did not properly initialize
this field, which would cause it to miss flows.  This commit sets the
value to zero, which allows any cookie.

Bug #8984

Signed-off-by: Justin Pettit <jpettit@nicira.com>
Reported-by: Luca Giraudo <lgiraudo@nicira.com>

Author: Justin Pettit

utilities/ovs-ofctl.c

@@ -1180,6 +1180,7 @@ read_flows_from_switch(struct vconn *vconn, enum nx_flow_format flow_format,
     cls_rule_init_catchall(&fsr.match, 0);
     fsr.out_port = OFPP_NONE;
     fsr.table_id = 0xff;
+    fsr.cookie = fsr.cookie_mask = htonll(0);
     request = ofputil_encode_flow_stats_request(&fsr, flow_format);
     send_xid = ((struct ofp_header *) request->data)->xid;
     send_openflow_buffer(vconn, request);