fs: prevent doing FALLOC_FL_ZERO_RANGE on append only file

Currently punch hole and collapse range fallocate operation are not
allowed on append only file. This should be case for zero range as well.
Fix it by allowing only pure fallocate (possibly with keep size set).

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>