cifs: optimize reconnect of nested links

There is no point going all the way back to the original dfs full path
if reconnect of tcon did not finish due a nested link found as newly
resolved target for the current referral.  So, just mark current
server for reconnect as we already set @current_fullpath to the new
dfs referral in update_server_fullpath().

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>