lora: asynchronous packet reception

Adds functionality to receive LoRa packets asynchronously. Reception
runs continuously until cancelled by another call to `lora_recv_async`.

Signed-off-by: Jordan Yates <jordan.yates@data61.csiro.au>

drivers/lora/sx127x.c

@@ -660,6 +660,7 @@ static const struct lora_driver_api sx127x_lora_api = {
 	.send = sx12xx_lora_send,
 	.send_async = sx12xx_lora_send_async,
 	.recv = sx12xx_lora_recv,
+	.recv_async = sx12xx_lora_recv_async,
 	.test_cw = sx12xx_lora_test_cw,
 };