firewire-lib: improve operation for oPCR

The value of 'payload' field don't need to change when establishing
connection to oPCR.

In IEC 61883-1, at '7.9 Plug control register modification rules',
there is no description about 'payload' field when establishing an
output connection:
'when an output plug becomes connected, the data rate field,
overhead_ID field, channel number field, broadcast connection
counter field and point-to-point connection counter field
shall be modified in the same compare_swap lock transaction;'

This commit is an answer for my previous commit:
0efc42cf24ceb535f77746012dcb0f028bce2298
bebob: fix condition in updating streams

Just my wrong coding.