net: ipv4: Use kfree_sensitive instead of kfree

key might contain private part of the key, so better use
kfree_sensitive to free it.

Fixes: 38320c70d282 ("[IPSEC]: Use crypto_aead and authenc in ESP")
Signed-off-by: Wang Ming <machel@vivo.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/esp4.c

@@ -1132,7 +1132,7 @@ static int esp_init_authenc(struct xfrm_state *x,
 	err = crypto_aead_setkey(aead, key, keylen);
 
 free_key:
-	kfree(key);
+	kfree_sensitive(key);
 
 error:
 	return err;