Fix panics when using iflib pseudo device support

[mmacy]

Summary

• _iflib_assert checks for values that are only relevant when doing queue management
• iflib_pseudo_register can return without dropping the context sx lock

Test Plan

ifconfig wg create with the fixes

[• hselasky]

Can you upload patch context?

[gallatin]

I'd prefer the check be moved inside _iflib_assert(), but that's just a nit.

[afedorov]

Are there any objections to not committing this?

[• hselasky]

No objections. Maybe split the commit into two when upstreaming and write a good commit message and don't forget to MFC.

[• hselasky]

@mmacy: Ping.

[mmacy]

I have further changes.