net__write buf should be const.

apps/db_dump/stubs.c

@@ -48,7 +48,7 @@ ssize_t net__read(struct mosquitto *mosq, void *buf, size_t count)
 	return 0;
 }
 
-ssize_t net__write(struct mosquitto *mosq, void *buf, size_t count)
+ssize_t net__write(struct mosquitto *mosq, const void *buf, size_t count)
 {
 	return 0;
 }

lib/net_mosq.c

@@ -995,7 +995,7 @@ ssize_t net__read(struct mosquitto *mosq, void *buf, size_t count)
 #endif
 }
 
-ssize_t net__write(struct mosquitto *mosq, void *buf, size_t count)
+ssize_t net__write(struct mosquitto *mosq, const void *buf, size_t count)
 {
 #ifdef WITH_TLS
 	int ret;

lib/net_mosq.h

@@ -69,7 +69,7 @@ int net__socket_nonblock(mosq_sock_t *sock);
 int net__socketpair(mosq_sock_t *sp1, mosq_sock_t *sp2);
 
 ssize_t net__read(struct mosquitto *mosq, void *buf, size_t count);
-ssize_t net__write(struct mosquitto *mosq, void *buf, size_t count);
+ssize_t net__write(struct mosquitto *mosq, const void *buf, size_t count);
 
 #ifdef WITH_TLS
 void net__print_ssl_error(struct mosquitto *mosq);