src/config.c: fix checkpatch.pl warnings

src/config.c: fix checkpatch.pl warnings

Fix most of the warnings/errors reported by Linux Kernel's
checkpatch.pl, except SPDX_LICENSE_TAG, USE_NEGATIVE_ERRNO types.
It also introduces reverse xmas tree local variable declarations
and header file reordering.

In summary, this patch fixes the following checkpatch.pl
recommendations:
total: 4 errors, 36 warnings, 1899 lines checked

Signed-off-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>