smb: client: allow more DFS referrals to be cached

In some DFS setups, a single DFS share may contain hundreds of DFS
links and increasing the DFS cache to allow more referrals to be
cached improves DFS failover as the client will likely find a cached
DFS referral when reconnecting and then avoiding unnecessary remounts.

Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>