caif: performance bugfix - allow radio stack to prioritize packets.

    In the CAIF Payload message the Packet Type indication must be set to
    UNCLASSIFIED in order to allow packet prioritization in the modem's
    network stack. Otherwise TCP-Ack is not prioritized in the modems
    transmit queue.

Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>