ra_mtu default value '0' causes error on config_parse_interface

[morohe]

Currently the default value of ra_mtu is 0, but it causes an error in parsing the config file.

config.c int config_parse_interface(void *data, size_t len, const char *name, bool overwrite)
~to line number 780~
if ((c = tb[IFACE_ATTR_RA_MTU])) {
        uint32_t ra_mtu = blobmsg_get_u32(c);
        if (ra_mtu < 1280 || ra_mtu > 65535)
                goto err;

                iface->ra_mtu = ra_mtu;
}

ra_mtu is checked with the following and it looks fine.

static int send_router_advert(struct interface *iface, const struct in6_addr *from)
~to line number 477~
if (mtu == 0)
        mtu = odhcpd_get_interface_config(iface->ifname, "mtu");

if (mtu < 1280)
        mtu = 1280;

To fix this issue, my suggest is

1. Add write to syslog on parse error detail in config_parse_interface.
2. Fix README.md ra_mtu default value is not zero, It's 1280.
3. Remove detailed error check on parse, if always checked at the time of use.
4. Or set to default value on error.

Thanks.

[morohe]

Sorry, I reported to bugs.openwrt.org. Close this issue.