HO prep: pass gsm_network to gsm_bts_alloc() already

Prepare for a future change that accesses bts->network during gsm_bts_alloc().

Currently, gsm_bts_alloc() takes a ctx parameter, and gsm_bts_alloc_register()
then gets the gsm_network pointer and sets bts->network to it. All callers
anyway pass gsm_network as ctx to gsm_bts_alloc(), and anything else would not
make sense anyway. So enforce passing exactly gsm_network to gsm_bts_alloc()
and already set the bts->network pointer from there.

Prepares-for: I00870a5828703cf397776668d3301c0c3a4e033a
Change-Id: Ie590c14aa08df4c4f345596b23e5226c5577057a
diff --git a/include/osmocom/bsc/gsm_data_shared.h b/include/osmocom/bsc/gsm_data_shared.h
index 45d67f6..d7514ca 100644
--- a/include/osmocom/bsc/gsm_data_shared.h
+++ b/include/osmocom/bsc/gsm_data_shared.h
@@ -810,7 +810,7 @@
 };
 
 
-struct gsm_bts *gsm_bts_alloc(void *talloc_ctx, uint8_t bts_num);
+struct gsm_bts *gsm_bts_alloc(struct gsm_network *net, uint8_t bts_num);
 struct gsm_bts *gsm_bts_num(struct gsm_network *net, int num);
 
 struct gsm_bts_trx *gsm_bts_trx_alloc(struct gsm_bts *bts);