mscsplit: gsm_network_init(): add explicit root talloc ctx

Decouple the root talloc context from libbsc's global talloc_bsc_ctx.

This allows to define the root talloc ctx from a main() scope, which in turn
helps decouple libmsc from libbsc.

Change-Id: I92f6b47b1eeea2e8f3fba66f25d7e708e5659f8a
diff --git a/openbsc/src/libbsc/bsc_init.c b/openbsc/src/libbsc/bsc_init.c
index 371ddee..06f4121 100644
--- a/openbsc/src/libbsc/bsc_init.c
+++ b/openbsc/src/libbsc/bsc_init.c
@@ -477,7 +477,7 @@
 	int rc;
 
 	/* initialize our data structures */
-	bsc_gsmnet = gsm_network_init(1, 1, mncc_recv);
+	bsc_gsmnet = gsm_network_init(tall_bsc_ctx, 1, 1, mncc_recv);
 	if (!bsc_gsmnet)
 		return -ENOMEM;