cifs: fsc should not default to "on"

I'm not sure why this was merged with this flag hardcoded on, but it
seems quite dangerous. Turn it off.

Also, mount.cifs hands unrecognized options off to the kernel so there
should be no need for changes there in order to support this.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>