bridge: track last used time in forwarding table

Adds tracking the last used time in forwarding table.
Rename ageing_timer to updated to better describe it.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc net/bridge/br_fdb.c
Simple merge

diff --cc net/bridge/br_input.c
Simple merge

diff --cc net/bridge/br_private.h
Simple merge