Add local bind address config

specific local address to bind in `config.json`:
`"local": "127.0.0.1"`

src/jconf.c

@@ -137,6 +137,10 @@ jconf_t *read_jconf(const char* file)
             {
                 conf.remote_port = to_string(value);
             }
+            else if (strcmp(name, "local") == 0)
+            {
+                conf.local_addr = to_string(value);
+            }
             else if (strcmp(name, "local_port") == 0)
             {
                 conf.local_port = to_string(value);

src/jconf.h

@@ -17,6 +17,7 @@ typedef struct
     int  remote_num;
     remote_addr_t remote_addr[MAX_REMOTE_NUM];
     char *remote_port;
+    char *local_addr;
     char *local_port;
     char *password;
     char *method;

src/local.c

@@ -876,6 +876,7 @@ int main (int argc, char **argv)
             }
         }
         if (remote_port == NULL) remote_port = conf->remote_port;
+        if (local_addr == NULL) local_addr = conf->local_addr;
         if (local_port == NULL) local_port = conf->local_port;
         if (password == NULL) password = conf->password;
         if (method == NULL) method = conf->method;

src/redir.c

@@ -729,6 +729,7 @@ int main (int argc, char **argv)
             }
         }
         if (remote_port == NULL) remote_port = conf->remote_port;
+        if (local_addr == NULL) local_addr = conf->local_addr;
         if (local_port == NULL) local_port = conf->local_port;
         if (password == NULL) password = conf->password;
         if (method == NULL) method = conf->method;