Renumber confusing value for GUC_UNIT_BYTE

Renumber confusing value for GUC_UNIT_BYTE

It had a power-of-two value, which looks right, and causes the other
values which aren't powers-of-two to look wrong.  But this is tested
for equality and not a bitwise test.

See also:
6e7baa322773ff8c79d4d8883c99fdeff5bfa679
https://www.postgresql.org/message-id/CAOG9ApEu8bXVwBxkOO9J7ZpM76TASK_vFMEEiCEjwhMmSLiaqQ%40mail.gmail.com

Author: Justin Pryzby <pryzby@telsasoft.com>
Discussion: https://www.postgresql.org/message-id/flat/20220720145220.GJ12702@telsasoft.com