net: kdoc struct net_device flags and priv_flags

net: kdoc struct net_device flags and priv_flags

We have documentation for these flags but they're scattered
all over the place. #defines don't allow documentation to be
written easily so to help to start bringing some documentation
together use the enums kdoc practice but keep the defines to
allow userspace to be able to #ifdef them.

I've verified the same values are assigned before and after
with a simple userspace test program [0] and checksumming the
output.

[0] http://drvbp1.linux-foundation.org/~mcgrof/kdoc/netdev_flags/

mcgrof@gnat ~/tmp $ ./check-flags | sha1sum
0ec5b6b1840aa3bb9ce464e61c564820871c92c3  -

Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>