net: qrtr: Support decoding incoming v2 packets

Add the necessary logic for decoding incoming messages of version 2 as
well. Also make sure there's room for the bigger of version 1 and 2
headers in the code allocating skbs for outgoing messages.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>