Convert an ovs-ofctl field name to ryu equivalent.

def ofp_ofctl_field_name_to_ryu(field):
    """Convert an ovs-ofctl field name to ryu equivalent."""
    mapped = _OXM_FIELD_OFCTL_ALIASES.get(field)
    if mapped:
        return mapped
    if field.endswith("_dst"):
        mapped = _OXM_FIELD_OFCTL_ALIASES.get(field[:-3] + "src")
        if mapped:
            return mapped[:-3] + "dst"
    return field