ksmbd: fix race condition from parallel smb2 logoff requests

If parallel smb2 logoff requests come in before closing door, running
request count becomes more than 1 even though connection status is set to
KSMBD_SESS_NEED_RECONNECT. It can't get condition true, and sleep forever.
This patch fix race condition problem by returning error if connection
status was already set to KSMBD_SESS_NEED_RECONNECT.

Reported-by: luosili <rootlab@huawei.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>