tipc: check the bearer min mtu properly when setting it by netlink

Checking the bearer min mtu with tipc_udp_mtu_bad() only works for
IPv4 UDP bearer, and IPv6 UDP bearer has a different value for the
min mtu. This patch checks with encap_hlen + TIPC_MIN_BEARER_MTU
for min mtu, which works for both IPv4 and IPv6 UDP bearer.

Note that tipc_udp_mtu_bad() is still used to check media min mtu
in __tipc_nl_media_set(), as m->mtu currently is only used by the
IPv4 UDP bearer as its default mtu value.

Fixes: 682cd3cf ("tipc: confgiure and apply UDP bearer MTU on running links")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/bearer.c

@@ -1151,8 +1151,8 @@ int __tipc_nl_bearer_set(struct sk_buff *skb, struct genl_info *info)
 				return -EINVAL;
 			}
 #ifdef CONFIG_TIPC_MEDIA_UDP
-			if (tipc_udp_mtu_bad(nla_get_u32
-					     (props[TIPC_NLA_PROP_MTU]))) {
+			if (nla_get_u32(props[TIPC_NLA_PROP_MTU]) <
+			    b->encap_hlen + TIPC_MIN_BEARER_MTU) {
 				NL_SET_ERR_MSG(info->extack,
 					       "MTU value is out-of-range");
 				return -EINVAL;