bitvec: Fix typo in the csn1 encoding code

We can curse about CSN.1 and 3GPP but I think we want to call
it cursor here.
log: "logging level everything" is a badly named option.

We tried to fix it but it isn't that easy. The original fix was
cd6ed82d1ff48f47ad9e33e6322df62896a76ed5 but we had to revert it
as "everything" is present/used in existing config files.

If we ever change the ABI we can make everything be something
that is > 0. For now use a wording that makes it obvious that
people should not use "everything".