Fix const-correctness for pointer variables to referred strings

src/netlog/netlog-conf.c

@@ -22,7 +22,7 @@ int config_parse_netlog_remote_address(const char *unit,
                                        void *data,
                                        void *userdata) {
         Manager *m = userdata;
-        char *e;
+        const char *e;
         int r;
 
         assert(filename);

src/share/path-util.c

@@ -327,7 +327,8 @@ bool path_is_safe(const char *p) {
 }
 
 char *file_in_same_dir(const char *path, const char *filename) {
-        char *e, *ret;
+        const char *e;
+        char *ret;
         size_t k;
 
         assert(path);

src/share/socket-util.c

@@ -33,7 +33,8 @@
 #include "util.h"
 
 int socket_address_parse(SocketAddress *a, const char *s) {
-        char *e, *n;
+        const char *e;
+        char *n;
         unsigned u;
         int r;