libcli/smb: send SMB2_NETNAME_NEGOTIATE_CONTEXT_ID

libcli/smb: send SMB2_NETNAME_NEGOTIATE_CONTEXT_ID

Note: Unlike the current documentation, the utf16 string
is not null-terminated, that matches Windows Server 1903
as a client.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14055
RN: Add the target server name of SMB 3.1.1 connections
as a hint to load balancers or servers with "multi-tenancy"
support.

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
(similar to commit 21f6cece543dd791e0f4636458bfe9819823420c)

Autobuild-User(v4-9-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-9-test): Wed Sep 11 13:27:24 UTC 2019 on sn-devel-144