At the beginning of C files, "vim" related directives have been turned
from "expandtab" to "noexpandtab" which is more convenient with
kernel-style identation.
This commit is the result of
  find . -type f -print0 | xargs -0 sed -i 's/expandtab/noexpandtab/g'
from the src/ directory.

/!\ it touches MANY files (so to say, all of them).
But changes are really minor and located at the very beginning of
the file, so probablility of merge conflicts is pretty small.