For UDP bearer, it seems insufficient for us to check MTU size only
when UDP bearer is enabled. Meanwhile, we should update MTU size for
UDP bearer with Path MTU discovery protocol once MTU size is changed
after bearer is enabled.
I should admit I'm not that familiar with tipc. Do you mean updating
b->mtu in response to PMTU updates of the route used for ub->ubsock?
The way I understand it, it would be certainly useful but it's not
directly related to the security issue this patch addresses as if there
are no updates, b->mtu cannot get too low and there is no risk of
a buffer overflow. In other words, reflecting PMTU updates is something
that can be IMHO left for later.