smb: client: don't retry IO on failed negprotos with soft mounts

If @server->tcpStatus is set to CifsNeedReconnect after acquiring
@ses->session_mutex in smb2_reconnect() or cifs_reconnect_tcon(), it
means that a concurrent thread failed to negotiate, in which case the
server is no longer responding to any SMB requests, so there is no
point making the caller retry the IO by returning -EAGAIN.

Fix this by returning -EHOSTDOWN to the callers on soft mounts.

Cc: David Howells <dhowells@redhat.com>
Reported-by: Jay Shin <jaeshin@redhat.com>
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>