AP_SerialManager: add support for fetching serial port by id

libraries/AP_SerialManager/AP_SerialManager.cpp

@@ -437,6 +437,15 @@ AP_SerialManager::SerialProtocol AP_SerialManager::get_mavlink_protocol(mavlink_
     return SerialProtocol_None;
 }
 
+// get_serial_by_id - gets serial by serial id
+AP_HAL::UARTDriver *AP_SerialManager::get_serial_by_id(uint8_t id)
+{
+    if (id < SERIALMANAGER_NUM_PORTS) {
+        return state[id].uart;
+    }
+    return nullptr;
+}
+
 // set_blocking_writes_all - sets block_writes on or off for all serial channels
 void AP_SerialManager::set_blocking_writes_all(bool blocking)
 {

libraries/AP_SerialManager/AP_SerialManager.h

@@ -147,6 +147,9 @@ public:
     // disable passthru by settings SERIAL_PASS2 to -1
     void disable_passthru(void);
 
+    // get Serial Port
+    AP_HAL::UARTDriver *get_serial_by_id(uint8_t id);
+
     // parameter var table
     static const struct AP_Param::GroupInfo var_info[];