The sealevel driver called sppp_attach before checking that board existed
and never called detach in the error path.

My change is to call sppp_attach from the netdev->init hook which happens
later in the process, and call detach from the uninit hook.

Also, changed the structure element 'netdev' to 'pppdev' to avoid confusion.

Here is the fix against 2.6.0-test5 latest