smb311 client: fix missing tcon check when mounting with linux/posix extensions

When mounting the same share twice, once with the "linux" mount parameter
(or equivalently "posix") and then once without (or e.g. with "nolinux"),
we were incorrectly reusing the same tree connection for both mounts.
This meant that the first mount of the share on the client, would
cause subsequent mounts of that same share on the same client to
ignore that mount parm ("linux" vs. "nolinux") and incorrectly reuse
the same tcon.

Cc: stable@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>