smb3: track the instance of each session for debugging

Each time we reconnect to the same server, bump an instance
counter (and display in /proc/fs/cifs/DebugData) to make it
easier to debug.

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

fs/cifs/smb2ops.c

@@ -110,6 +110,8 @@ smb2_set_credits(struct TCP_Server_Info *server, const int val)
 {
 	spin_lock(&server->req_lock);
 	server->credits = val;
+	if (val == 1)
+		server->reconnect_instance++;
 	spin_unlock(&server->req_lock);
 }