AP_HAL: added set_size() to RingBuffer API

libraries/AP_HAL/utility/RingBuffer.cpp

@@ -18,6 +18,18 @@ ByteBuffer::~ByteBuffer(void)
     delete [] buf;
 }
 
+/*
+  caller is responsible for locking in set_size()
+ */
+void ByteBuffer::set_size(uint32_t _size)
+{
+    uint8_t *oldbuf = buf;
+    head = tail = 0;
+    size = _size;
+    buf = new uint8_t[size];
+    delete [] oldbuf;
+}
+
 uint32_t ByteBuffer::available(void) const
 {
     uint32_t _tail;

libraries/AP_HAL/utility/RingBuffer.h

@@ -55,6 +55,9 @@ public:
     // return size of ringbuffer
     uint32_t get_size(void) const { return size; }
 
+    // set size of ringbuffer, caller responsible for locking
+    void set_size(uint32_t size);
+    
     // advance the read pointer (discarding bytes)
     bool advance(uint32_t n);