sgsn_main: add comment about exit statement never reached
diff --git a/openbsc/src/gprs/sgsn_main.c b/openbsc/src/gprs/sgsn_main.c
index bfa2e52..fa61e0e 100644
--- a/openbsc/src/gprs/sgsn_main.c
+++ b/openbsc/src/gprs/sgsn_main.c
@@ -281,5 +281,6 @@
 			exit(3);
 	}
 
+	/* not reached */
 	exit(0);
 }