ixgbe: avoid sleeping allocation in ixgbe_ipsec_vf_add_sa()

Change kzalloc() flags used in ixgbe_ipsec_vf_add_sa() to GFP_ATOMIC, to
avoid sleeping in IRQ context.

Dan Carpenter, with the help of Smatch, has found following issue:
The patch eda0333ac293: "ixgbe: add VF IPsec management" from Aug 13,
2018 (linux-next), leads to the following Smatch static checker
warning: drivers/net/ethernet/intel/ixgbe/ixgbe_ipsec.c:917 ixgbe_ipsec_vf_add_sa()
warn: sleeping in IRQ context

The call tree that Smatch is worried about is:
ixgbe_msix_other() <- IRQ handler
-> ixgbe_msg_task()
-> ixgbe_rcv_msg_from_vf()
-> ixgbe_ipsec_vf_add_sa()

Fixes: eda0333ac293 ("ixgbe: add VF IPsec management")
Reported-by: Dan Carpenter <[e-mail]>
Link: https://lore.kernel.org/intel-wired-lan/[e-mail]
Reviewed-by: Michal Kubiak <[e-mail]>
Signed-off-by: Przemek Kitszel <[e-mail]>
Reviewed-by: Shannon Nelson <[e-mail]>
Tested-by: Pucha Himasekhar Reddy <[e-mail]> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <[e-mail]>

drivers/net/ethernet/intel/ixgbe/ixgbe_ipsec.c

···
 		goto err_out;
 	}
 
-	xs = kzalloc(sizeof(*xs), GFP_KERNEL);
+	algo = xfrm_aead_get_byname(aes_gcm_name, IXGBE_IPSEC_AUTH_BITS, 1);
+	if (unlikely(!algo)) {
+		err = -ENOENT;
+		goto err_out;
+	}
+
+	xs = kzalloc(sizeof(*xs), GFP_ATOMIC);
 	if (unlikely(!xs)) {
 		err = -ENOMEM;
 		goto err_out;
···
 		memcpy(&xs->id.daddr.a4, sam->addr, sizeof(xs->id.daddr.a4));
 	xs->xso.dev = adapter->netdev;
 
-	algo = xfrm_aead_get_byname(aes_gcm_name, IXGBE_IPSEC_AUTH_BITS, 1);
-	if (unlikely(!algo)) {
-		err = -ENOENT;
-		goto err_xs;
-	}
-
 	aead_len = sizeof(*xs->aead) + IXGBE_IPSEC_KEY_BITS / 8;
-	xs->aead = kzalloc(aead_len, GFP_KERNEL);
+	xs->aead = kzalloc(aead_len, GFP_ATOMIC);
 	if (unlikely(!xs->aead)) {
 		err = -ENOMEM;
 		goto err_xs;