smb: client: optimize referral walk on failed link targets

If a link referral request sent to root server was successful but
client failed to connect to all link targets, there is no need to
retry same link referral on a different root server.  Set an end
marker for the DFS root referral so the client will not attempt to
re-send link referrals to different root servers on failures.

Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>