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.

Change-Id: Ib5bc662d38c554d66fc5049421a436bfd384ff75
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Patch-mainline: netdev @ 06/09/17, 23:03
Signed-off-by: Chris Lew <clew@codeaurora.org>