tipc: remove SS_CONNECTED sock state

In this commit, we replace references to sock->state SS_CONNECTE
with sk_state TIPC_ESTABLISHED.

Finally, the sock->state is no longer explicitly used by tipc.
The FSM below is for various types of connection oriented sockets.

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 |<--+
                    +--------------------+

Signed-off-by: Parthasarathy Bhuvaragan <parthasarathy.bhuvaragan@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>