Enabling the SDI-12 power line while the modem is on seems to make the modem lose state

The current firmware that seems to work fine on the older boards switches the modem on, connects to the network, gets the time, and then brings up the packet switched layer.

Next it enables the SDI-12 power, scans the SDI-12 bus, and reads any sensors found and disables the SDI-12 power.

Finally it uses the modem's MQTT stack to send the message.

The modem seems to lose some state on the new boards with this sequence. The network connection LED goes out temporarily when the SDI-12 power is enabled, and then the MQTT login command fails after the sensors are read.

As a test the firmware was changed to enable the SDI-12 power line at boot and then leave it on the entire time, and no sensors were scanned or read. The modem could then do the MQTT uplinks.

The next test will be to scan and read the sensors and see if it still works.