Fix typo and reduce allocation overhead of RTP retransmission requests.

    int32_t blp = 0;

    sp<ABuffer> buf = new ABuffer(1500);

    sp<ABuffer> buf = new ABuffer(16);

    buf->setRange(0, 0);

    uint8_t *ptr = buf->data();

    ptr[0] = 0x80 | 1;  // generic NACK

    ptr[1] = 205;  // RTPFB

    ptr[1] = 205;  // TSFB

    ptr[2] = 0;

    ptr[3] = 3;

    ptr[4] = 0xde;  // sender SSRC