cifs: client: force multichannel=off when max_channels=1

cifs: client: force multichannel=off when max_channels=1

Previously, specifying both multichannel and max_channels=1 as mount
options would leave multichannel enabled, even though it is not
meaningful when only one channel is allowed. This led to confusion and
inconsistent behavior, as the client would advertise multichannel
capability but never establish secondary channels.

Fix this by forcing multichannel to false whenever max_channels=1,
ensuring the mount configuration is consistent and matches user intent.
This prevents the client from advertising or attempting multichannel
support when it is not possible.

Signed-off-by: Rajasi Mandal <rajasimandal@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>