lib/, src/: Use SNPRINTF() instead of its pattern

lib/, src/: Use SNPRINTF() instead of its pattern

The variable declarations for the buffers have been aligned in this
commit, so that they appear in the diff, making it easier to review.

Some important but somewhat tangent changes included in this commit:

-  lib/nss.c: The size was being defined as 65, but then used as 64.
   That was a bug, although not an important one; we were just wasting
   one byte.  Fix that while we replace snprintf() by SNPRINTF(), which
   will get the size from sizeof(), and thus will use the real size.

Signed-off-by: Alejandro Colomar <alx@kernel.org>