sgsn init: pass sgsn_config pointer to sgsn_vty_init(), not sgsn_parse_config

In an upcoming commit, sgsn_vty_init() will require access to the global sgsn
config struct to initialize a generic VTY command with the proper config
destination address, see Change-Id I5b5b6a9678b458affa86800afb1ec726e66eed88.

Change-Id: Ie6b6e5422987586531a898e0c5b867623dbecb0f
diff --git a/include/openbsc/sgsn.h b/include/openbsc/sgsn.h
index 1ede2c9..1ed1583 100644
--- a/include/openbsc/sgsn.h
+++ b/include/openbsc/sgsn.h
@@ -140,8 +140,8 @@
 
 /* sgsn_vty.c */
 
-int sgsn_vty_init(void);
-int sgsn_parse_config(const char *config_file, struct sgsn_config *cfg);
+int sgsn_vty_init(struct sgsn_config *cfg);
+int sgsn_parse_config(const char *config_file);
 
 /* sgsn.c */