MIXERIOCLOADBUF ioctl: remove unnecessary string length restriction

mixer.cpp ensures the string is null-terminated (buffer length is 2048).

src/drivers/dshot/dshot.cpp

@@ -1070,7 +1070,7 @@ DShotOutput::pwm_ioctl(file *filp, int cmd, unsigned long arg)
 
 	case MIXERIOCLOADBUF: {
 			const char *buf = (const char *)arg;
-			unsigned buflen = strnlen(buf, 1024);
+			unsigned buflen = strlen(buf);
 			ret = _mixing_output.loadMixerThreadSafe(buf, buflen);
 
 			break;

src/drivers/mkblctrl/mkblctrl.cpp

@@ -1052,7 +1052,7 @@ MK::pwm_ioctl(file *filp, int cmd, unsigned long arg)
 
 	case MIXERIOCLOADBUF: {
 			const char *buf = (const char *)arg;
-			unsigned buflen = strnlen(buf, 1024);
+			unsigned buflen = strlen(buf);
 
 			if (_mixers == nullptr) {
 				_mixers = new MixerGroup(control_callback, (uintptr_t)&_controls);

src/drivers/pwm_out_sim/PWMSim.cpp

@@ -219,7 +219,7 @@ PWMSim::ioctl(device::file_t *filp, int cmd, unsigned long arg)
 
 	case MIXERIOCLOADBUF: {
 			const char *buf = (const char *)arg;
-			unsigned buflen = strnlen(buf, 1024);
+			unsigned buflen = strlen(buf);
 			ret = _mixing_output.loadMixerThreadSafe(buf, buflen);
 			break;
 		}

src/drivers/px4fmu/fmu.cpp

@@ -1470,7 +1470,7 @@ PX4FMU::pwm_ioctl(file *filp, int cmd, unsigned long arg)
 
 	case MIXERIOCLOADBUF: {
 			const char *buf = (const char *)arg;
-			unsigned buflen = strnlen(buf, 1024);
+			unsigned buflen = strlen(buf);
 			ret = _mixing_output.loadMixerThreadSafe(buf, buflen);
 			update_pwm_trims();
 

src/drivers/px4io/px4io.cpp

@@ -2704,7 +2704,7 @@ PX4IO::ioctl(file *filep, int cmd, unsigned long arg)
 
 	case MIXERIOCLOADBUF: {
 			const char *buf = (const char *)arg;
-			ret = mixer_send(buf, strnlen(buf, 2048));
+			ret = mixer_send(buf, strlen(buf));
 			break;
 		}
 

src/drivers/uavcan/uavcan_main.cpp

@@ -1099,7 +1099,7 @@ UavcanNode::ioctl(file *filp, int cmd, unsigned long arg)
 
 	case MIXERIOCLOADBUF: {
 			const char *buf = (const char *)arg;
-			unsigned buflen = strnlen(buf, 1024);
+			unsigned buflen = strlen(buf);
 
 			if (_mixers == nullptr) {
 				_mixers = new MixerGroup(control_callback, (uintptr_t)_controls);