Fix compilation with MG_DISABLE_HTTP_WEBSOCKET

Make restful_server and netcat examples compilation tests:
 - netcat doesn't use HTTP, compile it with MG_DISABLE_HTTP
 - restful_server doesn't use websocket, compile it with
   MG_DISABLE_HTTP_WEBSOCKET

h/t @labourcier, cesanta/mongoose#665

PUBLISHED_FROM=4494ac3cbd81e8314beb557ab301b4b44c4afb89

examples/netcat/Makefile

 PROG = nc
-MODULE_CFLAGS=-DMG_ENABLE_THREADS
+MODULE_CFLAGS=-DMG_ENABLE_THREADS -DMG_DISABLE_HTTP
 SSL_LIB=openssl
 include ../examples.mk

examples/restful_server/Makefile

 PROG = restful_server
+MODULE_CFLAGS=-DMG_ENABLE_THREADS -DMG_DISABLE_HTTP_WEBSOCKET
 include ../examples.mk

mongoose.c

@@ -5146,8 +5146,9 @@ void mg_http_handler(struct mg_connection *nc, int ev, void *ev_data) {
         mg_call(nc, nc->handler, MG_EV_WEBSOCKET_HANDSHAKE_DONE, NULL);
         mg_websocket_handler(nc, MG_EV_RECV, ev_data);
       }
+    }
 #endif /* MG_DISABLE_HTTP_WEBSOCKET */
-    } else if (hm->message.len <= io->len) {
+    else if (hm->message.len <= io->len) {
       int trigger_ev = nc->listener ? MG_EV_HTTP_REQUEST : MG_EV_HTTP_REPLY;
 
 /* Whole HTTP message is fully buffered, call event handler */
@@ -7764,6 +7765,7 @@ struct mg_connection *mg_connect_http(struct mg_mgr *mgr,
                              post_data);
 }
 
+#ifndef MG_DISABLE_HTTP_WEBSOCKET
 struct mg_connection *mg_connect_ws_opt(struct mg_mgr *mgr,
                                         mg_event_handler_t ev_handler,
                                         struct mg_connect_opts opts,
@@ -7792,6 +7794,7 @@ struct mg_connection *mg_connect_ws(struct mg_mgr *mgr,
   memset(&opts, 0, sizeof(opts));
   return mg_connect_ws_opt(mgr, ev_handler, opts, url, protocol, extra_headers);
 }
+#endif /* MG_DISABLE_HTTP_WEBSOCKET */
 
 size_t mg_parse_multipart(const char *buf, size_t buf_len, char *var_name,
                           size_t var_name_len, char *file_name,

mongoose.h

@@ -2127,10 +2127,12 @@ struct mg_http_multipart_part {
 #define MG_EV_HTTP_CHUNK 102   /* struct http_message * */
 #define MG_EV_SSI_CALL 105     /* char * */
 
+#ifndef MG_DISABLE_HTTP_WEBSOCKET
 #define MG_EV_WEBSOCKET_HANDSHAKE_REQUEST 111 /* NULL */
 #define MG_EV_WEBSOCKET_HANDSHAKE_DONE 112    /* NULL */
 #define MG_EV_WEBSOCKET_FRAME 113             /* struct websocket_message * */
 #define MG_EV_WEBSOCKET_CONTROL_FRAME 114     /* struct websocket_message * */
+#endif
 
 #ifdef MG_ENABLE_HTTP_STREAMING_MULTIPART
 #define MG_EV_HTTP_MULTIPART_REQUEST 121 /* struct http_message */
@@ -2184,6 +2186,7 @@ struct mg_http_multipart_part {
  */
 void mg_set_protocol_http_websocket(struct mg_connection *nc);
 
+#ifndef MG_DISABLE_HTTP_WEBSOCKET
 /*
  * Send websocket handshake to the server.
  *
@@ -2289,6 +2292,7 @@ void mg_send_websocket_framev(struct mg_connection *nc, int op_and_flags,
  */
 void mg_printf_websocket_frame(struct mg_connection *nc, int op_and_flags,
                                const char *fmt, ...);
+#endif /* MG_DISABLE_HTTP_WEBSOCKET */
 
 /*
  * Send buffer `buf` of size `len` to the client using chunked HTTP encoding.