s4:winbind: don't leak libnet_context into the main event context

s4:winbind: don't leak libnet_context into the main event context

This needs to be a talloc child of struct wbsrv_domain
otherwise the cleanup of a broken connection doesn't work.

The following command can trigger the leak on a domain controller.

root@dc:~/samba# ls -l /var/lib/samba/sysvol/samba.private/
total 16
drwxrwx---+ 5 root 3000000 4096 May 14 14:46 Policies
drwxrwx---+ 2 root 3000000 4096 May 14 11:45 scripts

gid 3000000 belongs to Builtin\Administrators.

The code triggers a ncacn_np: connection to the local smbd
and complains that domain BUILTIN is not available:

[2013/05/29 17:28:03,  2] ../source4/winbind/wb_init_domain.c:376(init_domain_recv_queryinfo)
  Expected domain name BUILTIN, DC dc.samba.private said SAMBA

In that case the connection was not closed, which is fixed by this commit.

Using ncalrpc: for all local SIDs and serving the BUILTIN domain is
a project for another day...

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Tue Jun  4 11:05:09 CEST 2013 on sn-devel-104