ofp-print: Fix memory leak at ofp_print_bundle_add().

ofp-print: Fix memory leak at ofp_print_bundle_add().

Call ds_put_and_free_cstr instead of ds_put_cstr to free msg.
Reported by test cases: 325, 326
    ofp_print_bundle_add (ofp-print.c:3027)
    ofp_to_string__ (ofp-print.c:3410)
    ofp_to_string (ofp-print.c:3465)
    ofp_print (ofp-print.c:3497)
    ofctl_ofp_print (ovs-ofctl.c:3818)
    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>
[blp@ovn.org simplified the code slightly]
Signed-off-by: Ben Pfaff <blp@ovn.org>
Signed-off-by: Ben Pfaff <blp@ovn.org>