candump: preserve silent mode with enabled log file output format

As seen in https://github.com/linux-can/can-utils/issues/150 the logfile
format switch ignores the silent mode switch.

Fix this by checking the silent mode when using logfile format on stdout.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>

candump.c

@@ -773,7 +773,7 @@ int main(int argc, char **argv)
 						max_devname_len, devname[idx], buf);
 				}
 
-				if (logfrmt) {
+				if ((logfrmt) && (silent == SILENT_OFF)){
 					char buf[CL_CFSZ]; /* max length */
 
 					/* print CAN frame in log file style to stdout */