getncchanges.c: Split sorting linked attributes into separate function

getncchanges.c: Split sorting linked attributes into separate function

Longer-term we want to split up the links so that they're sent over
multiple GetNCChanges response messages. So it makes sense to split this
code out into its own function. In the short-term, this removes some of
the complexity from dcesrv_drsuapi_DsGetNCChanges() so that the function
is not quite so big.

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>