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/ipaccess/ipaccess-config.c b/openbsc/src/ipaccess/ipaccess-config.c
index 31da056..9e3a471 100644
--- a/openbsc/src/ipaccess/ipaccess-config.c
+++ b/openbsc/src/ipaccess/ipaccess-config.c
@@ -983,7 +983,7 @@
 	}
 	libosmo_abis_init(tall_ctx_config);
 
-	bsc_gsmnet = gsm_network_init(1, 1, NULL);
+	bsc_gsmnet = gsm_network_init(tall_bsc_ctx, 1, 1, NULL);
 	if (!bsc_gsmnet)
 		exit(1);