ext4: enable punch hole for bigalloc

After applied this commit (d23142c6

), ext4 has supported punch hole for
a file system with bigalloc feature.  But we forgot to enable it.  This
commit fixes it.

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