ext4: fix COLLAPSE RANGE test for bigalloc file systems
Blocks in collapse range should be collapsed per cluster unit when
bigalloc is enable. If bigalloc is not enable, EXT4_CLUSTER_SIZE will
be same with EXT4_BLOCK_SIZE.
With this bug fixed, patch enables COLLAPSE_RANGE for bigalloc, which
fixes a large number of xfstest failures which use fsx.