bsc: Address warnings about implicit declarations

osmo_bsc_main.c: In function ‘main’:
osmo_bsc_main.c:398:2: warning: implicit declaration of function ‘bts_init’ [-Wimplicit-function-declaration]
osmo_bsc_main.c:399:2: warning: implicit declaration of function ‘libosmo_abis_init’ [-Wimplicit-function-declaration]
osmo_bsc_main.c:418:2: warning: implicit declaration of function ‘bsc_bootstrap_network’ [-Wimplicit-function-declaration]
diff --git a/openbsc/src/osmo-bsc/osmo_bsc_main.c b/openbsc/src/osmo-bsc/osmo_bsc_main.c
index 9a799c0..1fe43d5 100644
--- a/openbsc/src/osmo-bsc/osmo_bsc_main.c
+++ b/openbsc/src/osmo-bsc/osmo_bsc_main.c
@@ -18,6 +18,7 @@
  *
  */
 
+#include <openbsc/bss.h>
 #include <openbsc/control_cmd.h>
 #include <openbsc/debug.h>
 #include <openbsc/gsm_data.h>
@@ -33,6 +34,8 @@
 #include <osmocom/core/talloc.h>
 #include <osmocom/gsm/protocol/gsm_12_21.h>
 
+#include <osmocom/abis/abis.h>
+
 #include <osmocom/sccp/sccp.h>
 
 #define _GNU_SOURCE