The queue limit of the broadcast link is being calculated base on initial
MTU. However, when MTU value changed (e.g manual changing MTU on NIC
device, MTU negotiation etc.,) we do not re-calculate queue limit.
This gives throughput does not reflect with the change.

So fix it by calling the function to re-calculate queue limit of the
broadcast link.

Acked-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Hoang Huu Le <hoang.h.le@dektech.com.au>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>