Reduce lock contention in kernel port subsystem.

* Replace ports list mutex with R/W-lock.

* Move team port list protection to separate array of mutexes.
  Relieve contention on sPortsLock by removing Team::port_list from its
  protected items. With this, set_port_owner() only needs to acquire the
  sPortsLock for reading.

* Add another hash table holding the ports by name. Used by find_port()
  so it doesn't have to iterate over the list anymore.

* Use slab-based memory allocator for port messages. sPortQuotaLock was
  acquired on every message send or receive and was thus another point
  of contention. The lock is not necessary anymore.

* Lock for port hashes and Port::lock are no longer locked in a nested
  fashion to reduce chances of blocking other threads.

* Make operations concurrency-safe by adding an atomically accessed
  Port::state which provides linearization points to port creation and
  deletion. Both operations are now divided into logical and physical
  parts, the logical part just updating the state and the physical part
  adding/remove it to/from the port hash and team port list.

* set_port_owner() is the only remaining function which still locks
  Port::lock and one or two of sTeamListLock[] in a nested fashion.
  Since it needs to move the port from one team list to another and
  change Port::owner, there's no way around.

* Ports are now reference counted to make accesses to already-deleted
  ports safe.

* Should fix #8007.

headers/private/kernel/port.h

@@ -36,6 +36,8 @@ void delete_owned_ports(Team* team);
 int32 port_max_ports(void);
 int32 port_used_ports(void);
 
+size_t port_team_link_offset();
+
 status_t select_port(int32 object, struct select_info *info, bool kernel);
 status_t deselect_port(int32 object, struct select_info *info, bool kernel);