system_information: use bitvec to generate frequency lists

We use a 1024-bit-sized bitvec to generate the BA and neighbor frequency list.

This bitvec is still generated from the list of all BTS's inside the BSC, but
this patch is the first step to generalize this, i.e. generate arbitrary
neighbor lists.
diff --git a/openbsc/src/gsm_data.c b/openbsc/src/gsm_data.c
index cdaba9e..3cf9e3c 100644
--- a/openbsc/src/gsm_data.c
+++ b/openbsc/src/gsm_data.c
@@ -169,6 +169,12 @@
 	bts->ms_max_power = 15;	/* dBm */
 	bts->si_common.cell_sel_par.cell_resel_hyst = 2; /* 4 dB */
 	bts->si_common.cell_sel_par.rxlev_acc_min = 0;
+	bts->si_common.neigh_list.data = bts->si_common.data.neigh_list;
+	bts->si_common.neigh_list.data_len =
+				sizeof(bts->si_common.data.neigh_list);
+	bts->si_common.cell_alloc.data = bts->si_common.data.cell_alloc;
+	bts->si_common.cell_alloc.data_len =
+				sizeof(bts->si_common.data.cell_alloc);
 
 	for (i = 0; i < ARRAY_SIZE(bts->gprs.nsvc); i++) {
 		bts->gprs.nsvc[i].bts = bts;