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_shared.c b/src/libcommon/gsm_data_shared.c
index 8992636..d792f3b 100644
--- a/src/libcommon/gsm_data_shared.c
+++ b/src/libcommon/gsm_data_shared.c
@@ -312,7 +312,7 @@
 	.initial_mcs = 6,
 };
 
-struct gsm_bts *gsm_bts_alloc(void *ctx)
+struct gsm_bts *gsm_bts_alloc(void *ctx, uint8_t bts_num)
 {
 	struct gsm_bts *bts = talloc_zero(ctx, struct gsm_bts);
 	int i;
@@ -320,6 +320,7 @@
 	if (!bts)
 		return NULL;
 
+	bts->nr = bts_num;
 	bts->num_trx = 0;
 	INIT_LLIST_HEAD(&bts->trx_list);
 	bts->ms_max_power = 15;	/* dBm */