nvmet-tcp: fixup hang in nvmet_tcp_listen_data_ready()

nvmet-tcp: fixup hang in nvmet_tcp_listen_data_ready()

When the socket is closed while in TCP_LISTEN a callback is run to
flush all outstanding packets, which in turns calls
nvmet_tcp_listen_data_ready() with the sk_callback_lock held.
So we need to check if we are in TCP_LISTEN before attempting
to get the sk_callback_lock() to avoid a deadlock.

Link: https://lore.kernel.org/linux-nvme/CAHj4cs-zu7eVB78yUpFjVe2UqMWFkLk8p+DaS3qj+uiGCXBAoA@mail.gmail.com/
Tested-by:  Yi Zhang <yi.zhang@redhat.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Hannes Reinecke <hare@kernel.org>
Signed-off-by: Keith Busch <kbusch@kernel.org>