increase ringbuffer size from 512 to 1024 bytes

As reported in https://osmocom.org/issues/4335, there appear to
be some cards / use cases in which the 512 byte sized ringbuffer is
insufficient.  As we do have free RAM available, we can easily
increase the buffer size, despite not entirely knowing yet why
it needs to be *that* large.

Change-Id: Ie713d614ec5b334e9058d5d430e4bb660f5b8b69
Closes: OS#4335

firmware/libcommon/include/ringbuffer.h

@@ -21,7 +21,7 @@
 #include <stdbool.h>
 #include <sys/types.h>
 
-#define RING_BUFLEN 512
+#define RING_BUFLEN 1024
 
 typedef struct ringbuf {
 	uint8_t buf[RING_BUFLEN];