Gateway: implement UART reception in bulk mode

[geonnave]

Description

1. receive a trigger byte, setup dma for 31 bytes and arm a timeout
2. if received 31 bytes, pass the 32 bytes to application, if not, eventually the timeout expires, and then you pass anything you have to the application

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Testing of Node / Gateway (if applicable)

• I tested this change with _10_ nodes and _1_ gateways.
• I let it run for the following amount of time: _5_ min

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Additional Notes