MEDIUM: stick-table: Add support of a factor for IN/OUT bytes rates

MEDIUM: stick-table: Add support of a factor for IN/OUT bytes rates

Add a factor parameter to stick-tables, called "brates-factor", that is
applied to in/out bytes rates to work around the 32-bits limit of the
frequency counters. Thanks to this factor, it is possible to have bytes
rates beyond the 4GB. Instead of counting each bytes, we count blocks
of bytes. Among other things, it will be useful for the bwlim filter, to be
able to configure shared limit exceeding the 4GB/s.

For now, this parameter must be in the range ]0-1024].