simtrace.h: Increased host to SIMtrace buf size

The host got stuck sometimes when large data frames had to be send
from the host program to SIMtrace. The printouts would just stop
if many large packets were received from the SIM card and needed
to be transferred to the mobile phone.
Increasing the buffer length removed the problem.
diff --git a/firmware/src_simtrace/simtrace.h b/firmware/src_simtrace/simtrace.h
index 2530ec7..ea2d401 100644
--- a/firmware/src_simtrace/simtrace.h
+++ b/firmware/src_simtrace/simtrace.h
@@ -8,7 +8,7 @@
 #define DATAIN      2
 #define INT         3
 
-#define BUFLEN  64
+#define BUFLEN  512
 
 #define PHONE_DATAOUT     4
 #define PHONE_DATAIN      5