Bluetooth: Add smp_ltk_sec_level() helper function

There are several places that need to determine the security level that
an LTK can provide. This patch adds a convenience function for this to
help make the code more readable.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index a08b077..3700dd8 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -1114,7 +1114,7 @@
 	if (!key)
 		return false;
 
-	if (sec_level > BT_SECURITY_MEDIUM && !key->authenticated)
+	if (smp_ltk_sec_level(key) < sec_level)
 		return false;
 
 	if (test_and_set_bit(HCI_CONN_ENCRYPT_PEND, &hcon->flags))