XIA/Serval: fix most format issues

This patch fixes most format issues found by
scripts/checkpatch.pl on Serval's code.

Some issues are ignored because they are not problems.
For example, warning "line over 80 characters" for a long string
is not an issue.
Nevertheless, some issues were not ignored because they require
quite a change, for example warning
"Too many leading tabs - consider code refactoring".