Use a sensible port timeout value for the Kenwood TS-850

This  back end  used a  480  second timeout  which effectively  blocks
retries.  The  long timeout  claimed to  be for  something to  do with
tuning  which I  assume is  related to  an auto  ATU blocking  rig CAT
responses.  The standard retry mechanism should cope with this without
resorting to an artificially extended timeout.

kenwood/ts850.c

@@ -110,7 +110,7 @@ const struct rig_caps ts850_caps = {
 	.serial_handshake =  RIG_HANDSHAKE_HARDWARE,
 	.write_delay =  0,
 	.post_write_delay =  100,
-	.timeout =  480000,  // When you tune a Kenwood, the reply is delayed until you stop.
+	.timeout =  500,
 	.retry =  10,
 
 	.has_get_func =  TS850_FUNC_ALL,