Run bind(2) system call in parallel.

Run bind(2) system call in parallel.

For protocols that care about locking, use the shared net lock to
call sobind().  Use the per socket rwlock together with shared net
lock.  This affects protocols UDP, raw IP, and divert.  Move the
inpcb mutex locking into soreceive(), it is only used there.  Add
a comment to describe the current inmplementation of inpcb locking.

OK mvs@ sashan@