[BRIDGE]: Fix problems with filtering and defragmentation.

[BRIDGE]: Fix problems with filtering and defragmentation.

Dave, this patch from Bart De Schuymer <bdschuym@pandora.be> fixes problems
when using filtering and defragmentation.  The bridge needs to enforce the
MTU restriction after going through the filtering chain not before, because
the incoming filter may have reassembled an IP packet, that then needs to
be fragmented on the output chain.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@redhat.com>