ldb: removing alloc from unpack_data

ldb: removing alloc from unpack_data

Making unpack flag LDB_UNPACK_DATA_FLAG_NO_DATA_ALLOC required
behaviour, since allocating data during unpack is slow and unnecessary
in all current usages. In any future unpack usage, if editing of
returned memory is required, some function that duplicates the message
should be used, such as one of the filter_attrs functions, or msg_copy.

Signed-off-by: Aaron Haslett <aaronhaslett@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>