caif: Protected in-flight packets using dev or sock refcont.

CAIF Socket Layer and ip-interface registers reference counters
in CAIF service layer. The functions sock_hold, sock_put and
dev_hold, dev_put are used by CAIF Stack to protect from freeing
memory while packets are in-flight.

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