ldb: introduce ldb_unpack_data_withlist to unpack partial list of attributes

ldb: introduce ldb_unpack_data_withlist to unpack partial list of attributes

When provided with non NULL list ldb_unpack_data_withlist will only
unpack attributes that are specified in the list (+ distinguished name)
ldb_unpack_data is changed to call ldb_unpack_data_withlist behind the
scene.

(for modifications found by testing, and re-indentation requested in review)
Signed-off-by: Adrian Cochrane <adrianc@catalyst.net.nz>
Sadly a signed-off-by was not available from Matthieu Patou for the original
version of this patch posted to samba-technical for comment, so instead:

(for supervision of Adrian)
Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>
BUG: https://bugzilla.samba.org/show_bug.cgi?id=11602