Destroy protocol control block before perform `so_q0' and `so_q' queues

Destroy protocol control block before perform `so_q0' and `so_q' queues
cleanup.

The dying socket is already unlinked from the file descriptor layer, but
still accessible from the stack or from the file system layer. We need to
unlink the socket to prevent concurrent connection when we unlocked dying
socket while we perform `so_q0' or `so_q' queues cleanup or while we
perform (*pr_detach)(). This unlocking will be appeared with the upcoming
fine grained locked sockets diffs.

ok bluhm@