bonding: fix xfrm state handling when clearing active slave

If the active slave is cleared manually the xfrm state is not flushed.
This leads to xfrm add/del imbalance and adding the same state multiple
times. For example when the device cannot handle anymore states we get:
 [ 1169.884811] bond0: (slave eni0np1): bond_ipsec_add_sa_all: failed to add SA
because it's filled with the same state after multiple active slave
clearings. This change also has a few nice side effects: user-space
gets a notification for the change, the old device gets its mac address
and promisc/mcast adjusted properly.

Fixes: 18cb261a ("bonding: support hardware encryption offload to slaves")
Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/bonding/bond_options.c

@@ -936,7 +936,7 @@ static int bond_option_active_slave_set(struct bonding *bond,
 	/* check to see if we are clearing active */
 	if (!slave_dev) {
 		netdev_dbg(bond->dev, "Clearing current active slave\n");
-		RCU_INIT_POINTER(bond->curr_active_slave, NULL);
+		bond_change_active_slave(bond, NULL);
 		bond_select_active_slave(bond);
 	} else {
 		struct slave *old_active = rtnl_dereference(bond->curr_active_slave);