inpcb: Remove a PCB from its LB group upon a subsequent error

[markj]

Summary

If a memory allocation failure causes bind to fail, we should take the
inpcb back out of its LB group since it's not prepared to handle
connections.

[glebius]

In the context of bind(2) we definitely can M_WAITOK. At what conditions is M_NOWAIT required?

[markj]

In D37027#840925, @glebius wrote:

In the context of bind(2) we definitely can M_WAITOK. At what conditions is M_NOWAIT required?

The inpcb mutex forces us to use M_NOWAIT here. Maybe those structures should be embedded in the port hash table instead. Though, right now we consume ~3MB per VNET jail for M_PCB mallocs.