iflib: allow clone detach if not yet init

[kevans]

Summary

If we hit an error during init, then we'll unwind our state and attempt
to detach the device -- don't block it.

This was discovered by creating a wg0 with missing parameters; said
failure ended up leaving this orphaned device in place and ended up
panicking the system upon enumeration of the dev.* sysctl space.

MFC after: 3 days

[markj]

This happens after an error from iflib_pseudo_register()?

[kevans]

In D29145#652735, @markj wrote:

This happens after an error from iflib_pseudo_register()?

Correct- the error path I was specifically seeing is iflib_clone_create() -> iflib_pseudo_register() -> IFDI_CLONEATTACH(); iflib_clone_create tries to delete the child but gets smacked with an EBUSY from this. I thought about setting IFC_IN_DETACH, but it's all barely-constructed at that point.

[markj]

In D29145#652747, @kevans wrote:

In D29145#652735, @markj wrote:

This happens after an error from iflib_pseudo_register()?

Correct- the error path I was specifically seeing is iflib_clone_create() -> iflib_pseudo_register() -> IFDI_CLONEATTACH(); iflib_clone_create tries to delete the child but gets smacked with an EBUSY from this. I thought about setting IFC_IN_DETACH, but it's all barely-constructed at that point.

Sure, I think this way is fine. Sorry for the breakage.