Make filenames variables "const".

babeld.c

@@ -65,7 +65,7 @@ int default_wired_hello_interval = -1;
 int resend_delay = -1;
 int random_id = 0;
 int do_daemonise = 0;
-char *logfile = NULL,
+const char *logfile = NULL,
     *pidfile = "/var/run/babeld.pid",
     *state_file = "/var/lib/babel-state";
 
@@ -100,7 +100,7 @@ main(int argc, char **argv)
     struct sockaddr_in6 sin6;
     int rc, fd, i, opt;
     time_t expiry_time, source_expiry_time, kernel_dump_time;
-    char *config_file = NULL;
+    const char *config_file = NULL;
     void *vrc;
     unsigned int seed;
     struct interface *ifp;

babeld.h

@@ -87,7 +87,7 @@ extern int default_wireless_hello_interval, default_wired_hello_interval;
 extern int resend_delay;
 extern int random_id;
 extern int do_daemonise;
-extern char *logfile, *pidfile, *state_file;
+extern const char *logfile, *pidfile, *state_file;
 extern int link_detect;
 extern int all_wireless;