random32: add prandom_u32_max and convert open coded users

CVE-2016-5696

Many functions have open coded a function that returns a random
number in range [0,N-1]. Under the assumption that we have a PRNG
such as taus113 with being well distributed in [0, ~0U] space,
we can implement such a function as uword t = (n*m')>>32, where
m' is a random number obtained from PRNG, n the right open interval
border and t our resulting random number, with n,m',t in u32 universe.

Lets go with Joe and simply call it prandom_u32_max(), although
technically we have an right open interval endpoint, but that we
have documented. Other users can further be migrated to the new
prandom_u32_max() function later on; for now, we need to make sure
to migrate reciprocal_divide() users for the reciprocal_divide()
follow-up fixup since their function signatures are going to change.

Joint work with Hannes Frederic Sowa.

Change-Id: Ib62946c0432a63345723df0d891186cd939bec09
Tracked-On: https://jira01.devtools.intel.com/browse/AW-2264


Cc: Jakub Zawadzki <darkjames-ws@darkjames.pl>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Reviewed-on: https://android.intel.com/545360


Reviewed-by: Mahe, Erwan <erwan.mahe@intel.com>
Reviewed-by: Dubray, SimonX <simonx.dubray@intel.com>
Tested-by: Mahe, Erwan <erwan.mahe@intel.com>
Reviewed-by: Tasayco Loarte, VictorX <victorx.tasayco.loarte@intel.com>
Reviewed-by: Maalem, Saadi <saadi.maalem@intel.com>