Upstream: network: Replace network_change() with __connman_network_disconnect()

Upstream: network: Replace network_change() with __connman_network_disconnect()

The network_change() function called when a network error is set will
disconnect a network driver identical to __connman_network_disconnect()
but without any error handling. Therefore the specific network_change()
function is better replaced with __connman_network_disconnect(). With
connman_network_set_error() now calling __connman_network_disconnect(),
the additional function call can now be removed from
connman_network_set_connected().

Also let the associating and connecting variables be handled by the
normal code paths and don't forcefully unset them when an error happens.

Commit ID: 7a3740c4c65be7915c36daaac9b1a611fa498a2

Change-Id: I3223a9d13207898aa64e2002912516d5ad64c150
Signed-off-by: Saurav Babu <saurav.babu@samsung.com>