Update MQTT subscribe example to add keep-alive (ping) packets
[lpc1224] / host /
drwxr-xr-x   ..
drwxr-xr-x - dtplug_protocol
drwxr-xr-x - lighthouse
drwxr-xr-x - rf_sub1G
drwxr-xr-x - sd_robotgrow
drwxr-xr-x - sd_translate
drwxr-xr-x - udpbridge