remove cmp_output_get_bandwidth_units(), add opcr_set_bandwidth_parameters()

According to IEC61883-1:
 - The channel and associated bandwidth as stored in an oPCR shall be allocated
during the entire time the corresponding output plug is connected.

 - When an output plug becomes connected the data rate field, overhead_ID field,
channel number field, the broadcast connection counter field, and the
point-to-point connection counter field shall be modified in the same
compare_swap lock transaction.

 - If the broadcast connection counter of an oPCR is modified from zero to one
while its point-to-point connection counter remains zero. the channel number
shall be modified in the same compare_swap lock transaction.

But there is some questions:
1. The implementation of current_bandwidth_overhead() sometimes returns a value over
   the range of overhead ID encoding. why?
2. Setting payload size is needless, why?
3. According to the spec, after bus reset, the bandwidth is calcurated with oPCR.
   The data rate and payload don't change but overhead_id is zero, why?

I need the latest specification than its first revision in 1998...