The RSSI values reported by LoRa transceiver can be less than -127. Therefore, `int8_t` is not enough. This commit defines the RSSI of `netdev_lora_rx_info` as `int16_t` and adapt the drivers accordingly (sx126x, sx127x). (cherry picked from commit 9955a35c639ca9441ad42d9b2838205bc30ed587)