ofp-actions: Avoid buffer overread in BUNDLE action decoding.

Reported-at: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=9052
Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Justin Pettit <jpettit@ovn.org>
parse_PUSH_MPLS(char *arg, struct ofpbuf *ofpacts,
                enum ofputil_protocol *usable_protocols OVS_UNUSED)
{
    uint16_t ethertype;
    char *error;

    error = str_to_u16(arg, "push_mpls", &ethertype);
    if (!error) {
        ofpact_put_PUSH_MPLS(ofpacts)->ethertype = htons(ethertype);
    }
    return error;
}

parse_PUSH_MPLS(char *arg, struct ofpbuf *ofpacts,
                enum ofputil_protocol *usable_protocols OVS_UNUSED)
{
    uint16_t ethertype;
    char *error;

    error = str_to_u16(arg, "push_mpls", &ethertype);
    if (!error) {
        ofpact_put_PUSH_MPLS(ofpacts)->ethertype = htons(ethertype);
    }
    return error;
}
