In the cc6ul we are not powering-off the supply of the XBee.
This is making that after a suspend/resume action the XBee
hangs due to ModemManager hasn't been stopped before the suspend.
Stopping ModemManager before going to suspend solves the issue.
https://onedigi.atlassian.net/browse/DEL-7701
Signed-off-by: Francisco Gil <francisco.gilmartinez@digi.com>