statvfs: fix bsize and frsize mixup

statvfs: fix bsize and frsize mixup

the block size (the real one) is the "fundamental file system block size" and
that is the frsize struct member in the statvfs struct. The bsize struct member
of the statvfs struct is *different* from the same named one of the statfs
struct.

See also http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_statvfs.h.html

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11810

Signed-off-by: Bjoern Jacke <bjacke@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User(master): Andreas Schneider <asn@cryptomilk.org>
Autobuild-Date(master): Thu Jan 10 09:40:06 CET 2019 on sn-devel-144