Support receiving SI13 from BTS

* store SI13 in BTS struct
* check and handle BCCH SAPI

Change-Id: I610a93ce23725b182ec14e3507331295bd542f74
Related: OS#2400
diff --git a/src/osmo-bts-sysmo/sysmo_l1_if.c b/src/osmo-bts-sysmo/sysmo_l1_if.c
index 9170972..1c5ecc9 100644
--- a/src/osmo-bts-sysmo/sysmo_l1_if.c
+++ b/src/osmo-bts-sysmo/sysmo_l1_if.c
@@ -10,6 +10,8 @@
 #include <osmocom/core/gsmtap.h>
 #include <osmocom/core/talloc.h>
 #include <osmocom/core/timer.h>
+#include <osmocom/gsm/protocol/gsm_04_08.h>
+
 #include <sysmo_l1_if.h>
 #include <gprs_debug.h>
 #include <pcu_l1_if.h>