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>

fs/cifs/cifs_debug.c

@@ -420,6 +420,11 @@ static int cifs_debug_data_proc_show(struct seq_file *m, void *v)
 				   from_kuid(&init_user_ns, ses->linux_uid),
 				   from_kuid(&init_user_ns, ses->cred_uid));
 
+			if (ses->dfs_root_ses) {
+				seq_printf(m, "\n\tDFS root session id: 0x%llx",
+					   ses->dfs_root_ses->Suid);
+			}
+
 			spin_lock(&ses->chan_lock);
 			if (CIFS_CHAN_NEEDS_RECONNECT(ses, 0))
 				seq_puts(m, "\tPrimary channel: DISCONNECTED ");