CVE-2023-53517 tipc: do not update mtu if msg_max is too small in mtu negotiation

In the Linux kernel, the following vulnerability has been resolved: tipc: do not update mtu if msgmax is too small in mtu negotiation When doing link mtu negotiation, a malicious peer may send Activate msg with a very small mtu, e.g. 4 in Shuang's testing, without checking for the minimum mtu,...