nvme-tcp: don't access released socket during error recovery

While the error recovery work is temporarily failing reconnect attempts,
running the 'nvme list' command causes a kernel NULL pointer dereference
by calling getsockname() with a released socket.

During error recovery work, the nvme tcp socket is released and a new one
created, so it is not safe to access the socket without proper check.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Fixes: 02c57a82 ("nvme-tcp: print actual source IP address through sysfs "address" attr")
Reviewed-by: Martin Belanger <martin.belanger@dell.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>