gutils: Use international symbol for bits

Currently, the project uses IEC symbols and/or SI symbols everywhere else (e.g., KiB and kB). However, when it comes to bits, it uses JEDEC symbols (e.g., b). This mixing of standards does not make sense, especially when JEDEC symbols seem to be deprecated (at least in this project).

Moreover, it is a huge point of confusion for everyday people who don't know the difference between bits and bytes to read stuff like Mbps (the old ad hoc abbreviation) and Mb/s as "megabytes per second" and the like. That's the whole reason the IEC has come up with its symbols in the first place so that they leave no room for confusion, with a clear distinction between B (for bytes) and bit (for bits). As such, this commit updates all bit symbols to use those from the IEC standard.