AP_Airspeed: add allocare method for periph

libraries/AP_Airspeed/AP_Airspeed.cpp

@@ -319,8 +319,15 @@ void AP_Airspeed::init()
     }
 #endif
 
+    if (enabled(0)) {
+        allocate();
+    }
+}
+
+void AP_Airspeed::allocate()
+{
     if (sensor[0] != nullptr) {
-        // already initialised
+        // already initialised, periph may call allocate several times to allow CAN detection
         return;
     }
 

libraries/AP_Airspeed/AP_Airspeed.h

@@ -67,8 +67,9 @@ public:
 
     void set_fixedwing_parameters(const class AP_FixedWing *_fixed_wing_parameters);
 
-
     void init(void);
+    void allocate();
+
 
     // indicate which bit in LOG_BITMASK indicates we should log airspeed readings
     void set_log_bit(uint32_t log_bit) { _log_bit = log_bit; }