[Tipc-discussion] Yet another version checked in

[Jon M. <jon...@er...>]

I think I have succeeded in making the port/transport level lock
handling somewhat easier to understand, without changing the
basic locking policy.

New:

1: Callbacks to socket.c (dispatcher/wakeup dipatcher) are now
    called with and return with the port-lock on.

2: Symmetry: A port or subscription is now always
    locked/unlocked in the same function.

3: No dual-purpose functions to the reference manager;
    ref_lock_acquire/ref_unlock_discard etc are now gone.
    The port lock is still located in the corresponding reference
    entry, though, and is accessed via easily comprehensible
    inline functions; port_lock()/port_unlock() etc.

4: Better comments about what the locks protect, and what
    the lock functions do.

I will continue with a similar work on the node locks in a few days,
but I would welcome some feedback first.

/Jon