net: qrtr: Use sk_buff->cb in receive path

Rather than parsing the header of incoming messages throughout the
implementation do it once when we retrieve the message and store the
relevant information in the "cb" member of the sk_buff.

This allows us to, in a later commit, decode version 2 messages into
this same structure.

Change-Id: I96c11f7ad781bdd916aa3e0103dd97c74a7b3b25
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>