In order to determine whether an SMBEcho request can be sent
we need to know that the socket is established (server tcpStatus == CifsGood)
AND that an SMB NegotiateProtocol has been sent (server maxBuf != 0).
Without the second check we can send an Echo request during reconnection
before the server can accept it.

CC: JG <jg@cms.ac>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>