Respect volume length when formatting ext4 when restoring

This is needed for device encryption to work properly (there must
be space for a 16 KB footer at the end of the partition, which is
usually specified by the length option).

And yes, the old signature of make_ext4fs was wrong, but worked
anyway because the related header was not included and the compiler
let it pass an as implicit delcaration.

Change-Id: Ied7ec70bebc120cc2917771f59eeaeb7ea76bf8d