libcommon: Fix log output for bts>0.

Fixes regression probably introduced in c696cc28.

For bts>0 logging doesn't show bts number correctly when printing lchan
identification string - it will always show it as "bts=0". The reason for
this is that the identification string is cached before bts->nr value is
set to a proper value.

This patch sets bts->nr as part of the first step of the bts structure
initialization, before caching happens thus making sure the cached
identification string is cached with the correct values.

Change-Id: I61c18a7f021fcb1ec00d34a745f4e3ab03416c2d
diff --git a/src/libcommon/gsm_data.c b/src/libcommon/gsm_data.c
index b5bf059..7be2240 100644
--- a/src/libcommon/gsm_data.c
+++ b/src/libcommon/gsm_data.c
@@ -254,12 +254,13 @@
 	if (!model && type != GSM_BTS_TYPE_UNKNOWN)
 		return NULL;
 
-	bts = gsm_bts_alloc(net);
+	bts = gsm_bts_alloc(net, net->num_bts);
 	if (!bts)
 		return NULL;
 
+	net->num_bts++;
+
 	bts->network = net;
-	bts->nr = net->num_bts++;
 	bts->type = type;
 	bts->model = model;
 	bts->bsic = bsic;