prepare gsm_data.h header file sharing with osmo-bts

This should not introduce any functional changes, it just re-arranges
some definitions in the header file, and introduces the ROLE_BSC
define that we enable for the BSC-specific fields.
diff --git a/openbsc/include/openbsc/transaction.h b/openbsc/include/openbsc/transaction.h
index c008a96..acb2e6c 100644
--- a/openbsc/include/openbsc/transaction.h
+++ b/openbsc/include/openbsc/transaction.h
@@ -5,6 +5,7 @@
 #include <openbsc/gsm_subscriber.h>
 #include <osmocom/core/linuxlist.h>
 #include <openbsc/gsm_04_11.h>
+#include <openbsc/mncc.h>
 
 /* One transaction */
 struct gsm_trans {