tipc: correct problems with misleading flags returned using poll()

Prevent TIPC from incorrectly setting returned flags to poll()
in the following cases:

- an unconnected socket no longer indicates that it is always readable

- an unconnected, connecting, or listening socket no longer indicates
  that it is always writable

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>