This fixes a bug introduced by f1d048c3
(conf.c: use f_simple_int() for assigning simple integer options):
we used ASSIGN_INT_FIELD for assigning values to variables shorter than
int, while the destination pointer was set to int *, so neighbouring
fields were overwritten.

Another commit in a non-merged branch adds a build-time check to
avoid repeating this bug, but field names changed, so let's avoid
cherry-picking it here at this point.
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>