macsec: ensure rx_sa is set when validation is disabled

macsec_decrypt() is not called when validation is disabled and so
macsec_skb_cb(skb)->rx_sa is not set; but it is used later in
macsec_post_decrypt(), ensure that it's always initialized.

Fixes: c09440f7 ("macsec: introduce IEEE 802.1AE driver")
Signed-off-by: Beniamino Galvani <bgalvani@redhat.com>
Acked-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/macsec.c

@@ -944,7 +944,6 @@ static struct sk_buff *macsec_decrypt(struct sk_buff *skb,
 	}
 
 	macsec_skb_cb(skb)->req = req;
-	macsec_skb_cb(skb)->rx_sa = rx_sa;
 	skb->dev = dev;
 	aead_request_set_callback(req, 0, macsec_decrypt_done, skb);
 
@@ -1172,6 +1171,8 @@ static rx_handler_result_t macsec_handle_frame(struct sk_buff **pskb)
 		}
 	}
 
+	macsec_skb_cb(skb)->rx_sa = rx_sa;
+
 	/* Disabled && !changed text => skip validation */
 	if (hdr->tci_an & MACSEC_TCI_C ||
 	    secy->validate_frames != MACSEC_VALIDATE_DISABLED)