gnrc_lorawan: add support for class C

[jia200x]

Contribution description

This PR adds support for Class C in GNRC LoRaWAN. To activate, enable the CONFIG_GNRC_LORAWAN_CLASS_C CFLAG.

With Class C LoRaWAN nodes keep the receiver on all the time and therefore show the lowest downlink latency. Class C is also supported by common LoRaWAN network servers (e.g TTN, Chirpstack).

Testing procedure

• Enable Class C support in the LoRaWAN Network Server (e.g TTN)
• Run examples/gnrc_lorawan with CFLAGS=-DCONFIG_GNRC_LORAWAN_CLASS_C. Join the network and transmit and uplink.
• Schedule a downlink to the LoRaWAN node. The node should indicate packet reception. Also, make sure that LoRaWAN class A still works as expected.

Issues/PRs references

Depends on #19342

[riot-ci]

Murdock results

:x: FAILED

fee9f45e7aa7132e2df977ed55cbd44cef88f32d examples/gnrc_lorawan: add class C comment to Makefile

Success	Failures	Total	Runtime
4006	0	8234	03m:17s

Artifacts