s3: Fix bug 8334, do not fork the echo handler for smb2

s3: Fix bug 8334, do not fork the echo handler for smb2

If a smb1 negprot negotiated smb2 we forked the echo responder. This will
eventually lead to a panic from

[2011/08/30 10:33:29.212578,  0, pid=3846917] smbd/smb2_server.c:243(smbd_smb2_request_create)
  Invalid SMB packet: first request: 0x0009

because from the echo responder we always read using the normal smb1 protocol
handling routine. If that is a bit down the smb2 stream, we get a non-negprot
packet and panic.

BTW, the echo responder is not required for smb2 anyway, Microsoft confirmed
that it probes the server liveness using TCP keepalives and not smb2 echo
requests.