Merege changes in Sentek branch

[eva-cerncic]

Apply changes currently only in Sentek branch to the main:

• Restore channel mask after region init on session restore Restore channel mask after region init on session restore #23
• Add support to set or lock dwell time via SMTC modem API Add support to set or lock dwell time via SMTC modem API #22
• Add support for setting join start bank and subsequent join attempts cycling through all banks Add support for setting join start bank and subsequent join attempts cycling through all banks #21