mke2fs: require the bigalloc feature explicity if the cluster size is set

mke2fs: require the bigalloc feature explicity if the cluster size is set

When cluster-size is specified without the bigalloc feature, mke2fs
will ignore this argument silently.  But user might think bigalloc
feature has been enabled unless they use the dumpe2fs command.  So now
we ask user to set bigalloc feature explicity when cluster-size is
enabled.  This can make sure that users understand what they are doing
because bigalloc might impact the performance for some workloads.

Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>