ovs-ofctl: Fix memory leak reported by valgrind.

ovs-ofctl: Fix memory leak reported by valgrind.

Test case: ovs-ofctl replace-flows with --bundle(376) reports two leaks:
    ofpbuf_new(ofpbuf.c:151)
    ofpraw_alloc_xid(ofp-msgs.c:533)
    ofpraw_alloc(ofp-msgs.c:525)
    ofputil_encode_flow_mod(ofp-util.c:2290)
    bundle_flow_mod__(ovs-ofctl.c:1312)
    ofctl_flow_mod__(ovs-ofctl.c:1331)
    ofctl_flow_mod_file.isra.13(ovs-ofctl.c:1365)
    ovs_cmdl_run_command(command-line.c:121)
    main(ovs-ofctl.c:135)
and
    ofpraw_alloc(ofp-msgs.c:525)
    ofputil_encode_flow_mod(ofp-util.c:2290)
    fte_make_flow_mod(ovs-ofctl.c:2936)
    ofctl_replace_flows(ovs-ofctl.c:2981)
    ovs_cmdl_run_command(command-line.c:121)
    main(ovs-ofctl.c:135)

Signed-off-by: William Tu <u9012063@gmail.com>
Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>
Co-authored-by: Daniele Di Proietto <diproiettod@vmware.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>