MNCC: clarify naming / rename mncc_recv() to int_mncc_recv()

the int_ perfix (internal) symbolizes that this is the internal
MNCC handler code, receiving messages from the MNCC interface point.
diff --git a/openbsc/src/bsc_hack.c b/openbsc/src/bsc_hack.c
index 0841ad2..66a9aaa 100644
--- a/openbsc/src/bsc_hack.c
+++ b/openbsc/src/bsc_hack.c
@@ -242,7 +242,7 @@
 	/* parse options */
 	handle_options(argc, argv);
 
-	rc = bsc_bootstrap_network(mncc_recv, config_file);
+	rc = bsc_bootstrap_network(int_mncc_recv, config_file);
 	if (rc < 0)
 		exit(1);
 	bsc_api_init(bsc_gsmnet, msc_bsc_api());