add BTS TYPE field to facilitate future non-BS11 BTS support

diff --git a/src/gsm_data.c b/src/gsm_data.c
index def7fff..834f213 100644
--- a/src/gsm_data.c
+++ b/src/gsm_data.c
@@ -98,6 +98,7 @@
 		
 		bts->network = net;
 		bts->nr = i;
+		bts->type = GSM_BTS_TYPE_BS11;
 
 		for (j = 0; j < BTS_MAX_TRX; j++) {
 			struct gsm_bts_trx *trx = &bts->trx[j];