When using multidialect negotiate (default or specifying vers=3.0 which
allows any smb3 dialect), fix how we check for an existing server session.
Before this fix if you mounted a second time to the same server (e.g. a
different share on the same server) we would only reuse the existing smb
session if a single dialect were requested (e.g. specifying vers=2.1 or vers=3.0
or vers=3.1.1 on the mount command). If a default mount (e.g. not
specifying vers=) is done then would always create a new socket connection
and SMB3 (or SMB3.1.1) session each time we connect to a different share
on the same server rather than reusing the existing one.

Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>