net-caif: add CAIF generic caif support functions

Support functions for the caif protocol stack:
cfcnfg.c        - CAIF Configuration Module used for
                  adding and removing drivers and connection
cfpkt_skbuff.c  - CAIF Packet layer (SKB helper functions)

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