Enable MQTT client by default

PUBLISHED_FROM=cb5d5afe166f637082d4b1d1bce5d9c263e91fd0

docs/overview/build-options/enabling-flags.md

@@ -4,7 +4,7 @@ title: Enabling flags
 
 - `MG_ENABLE_SSL` Enable [SSL/TLS support](https://docs.cesanta.com/mongoose/master/#/http/ssl.md/) (OpenSSL API)
 - `MG_ENABLE_IPV6` Enable IPv6 support
-- `MG_ENABLE_MQTT` enable [MQTT client](https://docs.cesanta.com/mongoose/master/#/mqtt/client_example.md/)
+- `MG_ENABLE_MQTT` enable [MQTT client](https://docs.cesanta.com/mongoose/master/#/mqtt/client_example.md/) (on by default, set to 0 to disable)
 - `MG_ENABLE_MQTT_BROKER` enable [MQTT broker](https://docs.cesanta.com/mongoose/master/#/mqtt/server_example.md/)
 - `MG_ENABLE_DNS_SERVER` enable DNS server
 - `MG_ENABLE_COAP` enable CoAP protocol

examples/mqtt_client/Makefile

 PROG = mqtt_client
-MODULE_CFLAGS = -DMG_ENABLE_MQTT -DMG_ENABLE_HTTP=0
+MODULE_CFLAGS = -DMG_ENABLE_HTTP=0
 SSL_LIB=openssl
 include ../examples.mk

mongoose.h

@@ -1584,7 +1584,7 @@ const char *c_strnstr(const char *s, const char *find, size_t slen);
 #endif
 
 #ifndef MG_ENABLE_MQTT
-#define MG_ENABLE_MQTT 0
+#define MG_ENABLE_MQTT 1
 #endif
 
 #ifndef MG_ENABLE_MQTT_BROKER