odp-util: Fix memory leak reported by valgrind.

odp-util: Fix memory leak reported by valgrind.

Test case: OVS datapath key parsing and formatting (377)
Return without freeing buf:
    xmalloc(util.c:112)
    ofpbuf_init(ofpbuf.c:124)
    parse_odp_userspace_action(odp-util.c:987)
    parse_odp_action(odp-util.c:1552)
    odp_actions_from_string(odp-util.c:1721)
    parse_actions(test-odp.c:132)

Test case: OVS datapath actions parsing and formatting (380)
Exit withtou uninit in test-odp.c
    xrealloc(util.c:123)
    ofpbuf_resize__(ofpbuf.c:243)
    ofpbuf_put_uninit(ofpbuf.c:364)
    nl_msg_put_uninit(netlink.c:178)
    nl_msg_put_unspec_uninit(netlink.c:216)
    nl_msg_put_unspec(netlink.c:243)
    parse_odp_key_mask_attr(odp-util.c:3974)
    odp_flow_from_string(odp-util.c:4151)
    parse_keys(test-odp.c:49)
    test_odp_main(test-odp.c:237)
    ovstest_wrapper_test_odp_main__(test-odp.c:251)
    ovs_cmdl_run_command(command-line.c:121)
    main(ovstest.c:132)

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>