cifs: change_conf needs to be called for session setup

Today we skip calling change_conf for negotiates and session setup
requests. This can be a problem for mchan as the immediate next call
after session setup could be due to an I/O that is made on the
mount point. For single channel, this is not a problem as
there will be several calls after setting up session.

This change enforces calling change_conf when the total credits contain
enough for reservations for echoes and oplocks. We expect this to happen
during the last session setup response. This way, echoes and oplocks are
not disabled before the first request to the server. So if that first
request is an open, it does not need to disable requesting leases.

Cc: <stable@vger.kernel.org>
Reviewed-by: Bharath SM <bharathsm@microsoft.com>
Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>