This patch adds support for different size MTU's to bridging.
It is useful for bridging Ethernet's with jumbo frames, etc.

The mtu of the bridge pseudo-device is maintained as the minimum
of all the underlying ports.  And when forwarding a frame through
the bridge, it will drop the frame if the outgoing port's MTU
is less than the frame size (as per 802 standard).
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@redhat.com>