sgsnemu: Fix gengetopt package name

gengetopt by default picks the program name from PACKAGE (autotools),
which is osmo-ggsn and is obviously wrong in case of sgsnemu.

After this patch, "sgsnemu --help" no longer shows "osmo-ggsn" but
"sgsnemu" at the top of the help text.

Change-Id: Ifabc2435a503ef71aa5a002ca46833f329068b37
diff --git a/sgsnemu/cmdline.c b/sgsnemu/cmdline.c
index 88210d7..d7be13a 100644
--- a/sgsnemu/cmdline.c
+++ b/sgsnemu/cmdline.c
@@ -27,8 +27,7 @@
 
 const char *gengetopt_args_info_purpose = "";
 
-const char *gengetopt_args_info_usage =
-    "Usage: " CMDLINE_PARSER_PACKAGE " [OPTIONS]...";
+const char *gengetopt_args_info_usage = "Usage: sgsnemu [OPTIONS]...";
 
 const char *gengetopt_args_info_versiontext = "";