Merge branch 'tipc-fixes'

Xin Long says:

====================
tipc: fix the mtu update in link mtu negotiation

This patchset fixes a crash caused by a too small MTU carried in the
activate msg. Note that as such malicious packet does not exist in
the normal env, the fix won't break any application

The 1st patch introduces a function to calculate the minimum MTU for
the bearer, and the 2nd patch fixes the crash with this helper. While
at it, the 3rd patch fixes the udp bearer mtu update by netlink with
this helper.
====================

Reviewed-by: Tung Nguyen <tung.q.nguyen@dektech.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>