bonding: fix null pointer deref in bond_ipsec_offload_ok

We must check if there is an active slave before dereferencing the pointer.

Fixes: 18cb261 ("bonding: support hardware encryption offload to slaves")
Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/bonding/bond_main.c

@@ -604,6 +604,8 @@ static bool bond_ipsec_offload_ok(struct sk_buff *skb, struct xfrm_state *xs)
 	bond = netdev_priv(bond_dev);
 	rcu_read_lock();
 	curr_active = rcu_dereference(bond->curr_active_slave);
+	if (!curr_active)
+		goto out;
 	real_dev = curr_active->dev;
 
 	if (BOND_MODE(bond) != BOND_MODE_ACTIVEBACKUP)