Add SPDX-License-Identifier to all source files

Change-Id: I9f2bc8c5d8a2c0bb0dd6caa4de5e2cb11be210e7
diff --git a/src/input/lapd_pcap.c b/src/input/lapd_pcap.c
index 7374694..77d4971 100644
--- a/src/input/lapd_pcap.c
+++ b/src/input/lapd_pcap.c
@@ -5,6 +5,8 @@
  * Author: Harald Welte <laforge@gnumonks.org>
  *         Pablo Neira Ayuso <pablo@gnumonks.org>
  *
+ * SPDX-License-Identifier: AGPL-3.0+
+ *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as published by
  * the Free Software Foundation; either version 3 of the License, or