getncchanges.c: Send linked attributes in each chunk

getncchanges.c: Send linked attributes in each chunk

Instead of sending all the linked attributes at the end, add a
configurable option to send the links in each replication chunk.

The benefits of this approach are:
- it can reduce memory overhead, as we don't have to keep all the links
in memory over the entire replication cycle.
- the client should never end up knowing about objects but not their
links. (Although we're not sure that this has actually resulted in
replication problems, i.e. missing links).

Note that until we support GET_TGT, this approach can mean we now send
a link where the client doesn't know about the target object, causing
the client to siliently drop that linked attribute. Hence, this option
is switched off by default.

Implementation-wise, this code works fairly the same as before. Instead
of sorting the entire getnc_state->la_sorted array at the end and then
splitting it up over chunks, we now split the links up over chunks and
then sort them when we copy them into the message. This should be OK, as
I believe the MS-DRSR Doc says the links in the message should be sorted
(rather than sorting *all* the links overall). Windows behaviour seems
to chunk the links based on USN and then sort them.

getnc_state->la_idx now tracks which links in getnc_state->la_list[]
have already been sent (instead of tracking getnc_state->la_sorted).
This means the la_sorted array no longer needs to be stored in
getnc_state and we can free the array's memory once we've copied the
links into the message. Unfortunately, the link_given/link_total debug
no longer reports the correct information, so I've moved these into
getncchanges_state struct (and now free the struct a bit later so it's
safe to reference in the debug).

The vampire_dc testenv has been updated to use this new behaviour.

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>
Autobuild-User(master): Douglas Bagnall <dbagnall@samba.org>
Autobuild-Date(master): Fri Sep 15 10:07:33 CEST 2017 on sn-devel-144