[copyright] add MIT license headers to .sh scripts where missing

Years are set according to 'git log' history

contrib/qos/tc.sh

@@ -1,3 +1,7 @@
+# Copyright (c) 2013 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
 #network interface on which to limit traffic
 IF="eth0"
 #limit of the network interface in question