cifs: return DFS root session id in DebugData

Return the DFS root session id in /proc/fs/cifs/DebugData to make it
easier to track which IPC tcon was used to get new DFS referrals for a
specific connection, and aids in debugging.

A simple output of it would be

  Sessions:
  1) Address: 192.168.1.13 Uses: 1 Capability: 0x300067   Session Status: 1
  Security type: RawNTLMSSP  SessionId: 0xd80000000009
  User: 0 Cred User: 0
  DFS root session id: 0x128006c000035

Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Cc: stable@vger.kernel.org # 6.2
Signed-off-by: Steve French <stfrench@microsoft.com>