WoBle fragment size getters drop the high byte from fragment sizes

[bzbarsky-apple]

In src/ble/WoBle.h, we have:

    inline void SetTxFragmentSize(uint8_t size) { mTxFragmentSize = size; };
    inline void SetRxFragmentSize(uint8_t size) { mRxFragmentSize = size; };

    uint16_t GetRxFragmentSize(void) { return mRxFragmentSize; };
    uint16_t GetTxFragmentSize(void) { return mTxFragmentSize; };
....
    uint16_t mRxFragmentSize;
...
    uint16_t mTxFragmentSize;

and various code passes uint16_t values to the setters. This silently drops the high byte of those values, which doesn't seem desirable.