tc/police: enable use of 64 bit burst parameter

tc/police: enable use of 64 bit burst parameter

	Modify tc police to permit burst sizes up to the limit of the
kernel API, which may exceed 4 GB of burst size at higher rates.

	 As presently implemented, the tc police burst option limits the
size of the burst to 4 GB in size.  This is a reasonable limit for the
rates common when this was developed.  However, the underlying
implementation of burst is expressed in terms of time at the specified
rate, and for higher rates, a burst size exceeding 4 GB is feasible
without modification to the kernel.

	The kernel API specifies the burst size as the number of "psched
ticks" needed to send the burst at the specified rate.  As each psched
tick is 64 nsec, the actual kernel limit on burst size is approximately
274.88 seconds (UINT_MAX * 64 / NSEC_PER_SEC).

	For example, at a rate of 10 Gbit/sec, the current 4 GB size limit
corresponds to just under 3.5 seconds.

	Additionally, overflows (burst values that exceed UINT_MAX psched
ticks) are now correctly detected, and flagged as an error, rather than
passing arbitrary psched tick values to the kernel.

Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Signed-off-by: David Ahern <dsahern@kernel.org>