net: Add CAN protocol family type used in socket CAN support

This commit adds PF_CAN and AF_CAN protocol family identifiers
that are used by BSD socket CAN support code.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Signed-off-by: Vipin Anand <vipin.anand@intel.com>