mscsplit: bsc_vty_init(): decouple from global bsc_gsmnet

Add an explicit gsm_network pointer instead of using the bsc_gsmnet global.
This allows passing a gsm_network struct from the main() scope, which helps to
decouple libmsc from libbsc.

Change-Id: I9e2c0d9c18d4cebb5efb71565ad84df2bc2e0251
diff --git a/openbsc/src/libbsc/bsc_vty.c b/openbsc/src/libbsc/bsc_vty.c
index 01eec23..cdcc011 100644
--- a/openbsc/src/libbsc/bsc_vty.c
+++ b/openbsc/src/libbsc/bsc_vty.c
@@ -4028,7 +4028,7 @@
 
 extern int bsc_vty_init_extra(void);
 
-int bsc_vty_init(const struct log_info *cat)
+int bsc_vty_init(const struct log_info *cat, struct gsm_network *network)
 {
 	cfg_ts_pchan_cmd.string =
 		vty_cmd_string_from_valstr(tall_bsc_ctx,