sgsnemu: relax check on length of IMSI cmdline arg.

Change-Id: I0374ff8773ae528c916fbee5f3f1efd89a5d2a08
diff --git a/sgsnemu/sgsnemu.c b/sgsnemu/sgsnemu.c
index c310164..002c2e4 100644
--- a/sgsnemu/sgsnemu.c
+++ b/sgsnemu/sgsnemu.c
@@ -492,7 +492,7 @@
 	}
 
 	/* imsi                                                            */
-	if (strlen(args_info.imsi_arg) != 15) {
+	if (strlen(args_info.imsi_arg) < 6 || strlen(args_info.imsi_arg) > 15) {
 		printf("Invalid IMSI\n");
 		return -1;
 	}