net: bridge: add helper to offload ageing time

The SWITCHDEV_ATTR_ID_BRIDGE_AGEING_TIME switchdev attr is actually set
when initializing a bridge port, and when configuring the bridge ageing
time from ioctl/netlink/sysfs.

Add a __set_ageing_time helper to offload the ageing time to physical
switches, and add the SWITCHDEV_F_DEFER flag since it can be called
under bridge lock.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index 26aec23..e2cd6d1 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -999,6 +999,7 @@ void __br_set_forward_delay(struct net_bridge *br, unsigned long t);
 int br_set_forward_delay(struct net_bridge *br, unsigned long x);
 int br_set_hello_time(struct net_bridge *br, unsigned long x);
 int br_set_max_age(struct net_bridge *br, unsigned long x);
+int __set_ageing_time(struct net_device *dev, unsigned long t);
 int br_set_ageing_time(struct net_bridge *br, clock_t ageing_time);