It's confusing, but f_bsize is not the value you're looking for; the
real block size is f_frsize. Fix all those bugs.
Also, the vast majority of clients are interested in the usable
disk space, not including reserved space.
Test: builds, boots
Bug: 36840579
Change-Id: Ib1470389afd49c14cab62282ec1e978ebb2c4791