Merge branch 'tipc-socket-layer-improvements'

Parthasarathy Bhuvaragan says:

====================
tipc: socket layer improvements

The following issues with the current socket layer hinders socket diagnostics
implementation, which led to this patch series.

1. tipc socket state is derived from multiple variables like
   sock->state, tsk->probing_state and tsk->connected. This style forces
   us to export multiple attributes to the user space, which has to be
   backward compatible.

2. Abuse of sock->state cannot be exported to user-space without
   requiring tipc specific hacks in the user-space.
   - For connection less (CL) sockets sock->state is overloaded to
     tipc state SS_READY.
   - For connection oriented (CO) listening socket sock->state is
     overloaded to tipc state SS_LISTEN.

This series is split into four:
1. Bug fixes in patch #1,2,3.
2. Minor cleanups in patch#4-5.
3. Express all tipc states using a single variable in patch#6-8.
4. Migrate the new tipc states to sk->sk_state in patch#9-16.

The figures below represents the FSM after this series:

Stream Server Listening Socket:
+-----------+       +-------------+
| TIPC_OPEN |------>| TIPC_LISTEN |
+-----------+       +-------------+

Stream Server Data Socket:
+-----------+       +------------------+
| TIPC_OPEN |------>| TIPC_ESTABLISHED |
+-----------+       +------------------+
                          ^   |
                          |   |
                          |   v
                    +--------------------+
                    | TIPC_DISCONNECTING |
                    +--------------------+

Stream Socket Client:
+-----------+       +-----------------+
| TIPC_OPEN |------>| TIPC_CONNECTING |------+
+-----------+       +-----------------+      |
                            |                |
                            |                |
                            v                |
                    +------------------+     |
                    | TIPC_ESTABLISHED |     |
                    +------------------+     |
                          ^   |              |
                          |   |              |
                          |   v              |
                    +--------------------+   |
                    | TIPC_DISCONNECTING |<--+
                    +--------------------+

NOTE:
This is just a base refractoring required for socket diagnostics.
TIPC socket diagnostics support will be introduced in a later series.

v2: - remove extra cast and parenthesis as suggested by David S. Miller in #4.
    - map new tipc state values to tcp states to address Eric Dumazet's concern,
      thus allow the usage of generic sk_* helpers. This is done in patch#10-15.
    - remove TIPC_PROBING state and replace it with probe_unacked flag in #11.
    - replace the TIPC_CLOSING state in v1 with sk_shutdown flag in #14.
    - introduce __tipc_shutdown() to avoid code duplication in #14.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>