move gsm_bts_num() to gsm_data_shared.[ch]

this way we can drop a copy of this function from osmo-bts.
diff --git a/openbsc/include/openbsc/gsm_data.h b/openbsc/include/openbsc/gsm_data.h
index 4338cd6..254feaf 100644
--- a/openbsc/include/openbsc/gsm_data.h
+++ b/openbsc/include/openbsc/gsm_data.h
@@ -332,8 +332,6 @@
 				     int (*mncc_recv)(struct gsm_network *, struct msgb *));
 int gsm_set_bts_type(struct gsm_bts *bts, enum gsm_bts_type type);
 
-struct gsm_bts *gsm_bts_num(struct gsm_network *net, int num);
-
 /* Get reference to a neighbor cell on a given BCCH ARFCN */
 struct gsm_bts *gsm_bts_neighbor(const struct gsm_bts *bts,
 				 uint16_t arfcn, uint8_t bsic);
diff --git a/openbsc/include/openbsc/gsm_data_shared.h b/openbsc/include/openbsc/gsm_data_shared.h
index 3abb38b..18db49d 100644
--- a/openbsc/include/openbsc/gsm_data_shared.h
+++ b/openbsc/include/openbsc/gsm_data_shared.h
@@ -741,8 +741,9 @@
 
 
 struct gsm_bts *gsm_bts_alloc(void *talloc_ctx);
-struct gsm_bts_trx *gsm_bts_trx_alloc(struct gsm_bts *bts);
+struct gsm_bts *gsm_bts_num(struct gsm_network *net, int num);
 
+struct gsm_bts_trx *gsm_bts_trx_alloc(struct gsm_bts *bts);
 struct gsm_bts_trx *gsm_bts_trx_num(const struct gsm_bts *bts, int num);
 
 
diff --git a/openbsc/src/libcommon/gsm_data.c b/openbsc/src/libcommon/gsm_data.c
index 5f7e32e..51444e7 100644
--- a/openbsc/src/libcommon/gsm_data.c
+++ b/openbsc/src/libcommon/gsm_data.c
@@ -150,21 +150,6 @@
 	return net;
 }
 
-struct gsm_bts *gsm_bts_num(struct gsm_network *net, int num)
-{
-	struct gsm_bts *bts;
-
-	if (num >= net->num_bts)
-		return NULL;
-
-	llist_for_each_entry(bts, &net->bts_list, list) {
-		if (bts->nr == num)
-			return bts;
-	}
-
-	return NULL;
-}
-
 /* Get reference to a neighbor cell on a given BCCH ARFCN */
 struct gsm_bts *gsm_bts_neighbor(const struct gsm_bts *bts,
 				 uint16_t arfcn, uint8_t bsic)
diff --git a/openbsc/src/libcommon/gsm_data_shared.c b/openbsc/src/libcommon/gsm_data_shared.c
index 1b0814c..8d5d0f8 100644
--- a/openbsc/src/libcommon/gsm_data_shared.c
+++ b/openbsc/src/libcommon/gsm_data_shared.c
@@ -132,6 +132,21 @@
 	return get_value_string(chreq_names, c);
 }
 
+struct gsm_bts *gsm_bts_num(struct gsm_network *net, int num)
+{
+	struct gsm_bts *bts;
+
+	if (num >= net->num_bts)
+		return NULL;
+
+	llist_for_each_entry(bts, &net->bts_list, list) {
+		if (bts->nr == num)
+			return bts;
+	}
+
+	return NULL;
+}
+
 struct gsm_bts_trx *gsm_bts_trx_alloc(struct gsm_bts *bts)
 {
 	struct gsm_bts_trx *trx = talloc_zero(bts, struct gsm_bts_trx);