AP_IOMCU: allow DSM input as pulses in iomcu

useful for receivers where DSM uses a normal servo plug

libraries/AP_IOMCU/iofirmware/rc.cpp

@@ -68,13 +68,10 @@ void AP_IOMCU_FW::rcin_serial_init(void)
                                SD_PARITY_ERROR);
     rcprotocol = AP_RCProtocol::get_instance();
 
-    // disable input for DSM and SBUS with pulses, we will use uarts
-    // for those. This allows us to use the RCIN port for a much wider
-    // range of protocols, relying on the 16 bit CRC on those
-    // protocols to keep them glitch free
+    // disable input for SBUS with pulses, we will use the UART for
+    // SBUS.
     rcprotocol->disable_for_pulses(AP_RCProtocol::SBUS);
     rcprotocol->disable_for_pulses(AP_RCProtocol::SBUS_NI);
-    rcprotocol->disable_for_pulses(AP_RCProtocol::DSM);
 }
 
 static struct {