iotests/264: Use iotests.sock_dir for socket creation

iotests/264: Use iotests.sock_dir for socket creation

If socket path is too long (longer than 108 bytes), socket can't be
opened.  This might lead to failure when test dir path is long enough.
Make sure socket is created in iotests.sock_dir to avoid such a case.

This commit basically aligns iotests/264 with the rest of iotests.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
Message-ID: <20240125135237.189493-1-andrey.drobyshev@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>