w1: optional bundling of netlink kernel replies

Applications can submit a set of commands in one packet to the kernel,
and in some cases it is required such as reading the temperature
sensor results.  This adds an option W1_CN_BUNDLE to the flags of
cn_msg to request the kernel to reply in one packet for efficiency.

The cn_msg flags now check for unknown flag values and return an error
if one is seen.  See "Proper handling of unknown flags in system
calls" http://lwn.net/Articles/588444/

This corrects the ack values returned as per the protocol standard,
namely the original ack for status messages and seq + 1 for all others
such as the data returned from a read.

Signed-off-by: David Fries <David@Fries.net>

Some of the common variable names have been standardized as follows.
struct cn_msg *cn
struct w1_netlink_msg *msg
struct w1_netlink_cmd *cmd
struct w1_master *dev

When an argument and a function scope variable would collide, add req_
to the argument.