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

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.

Reviewed by: glebius
MFC after: 2 weeks
Sponsored by: Modirum MDPay
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D37027