QBluetoothSocket - fix open mode on OS X

When a socket created (by server) from a notification (channel) - set
d_ptr's openMode (even with a given channel it happens that we receive
channel open callback asynchronously).

Change-Id: Ia2c461d4146645c661e25245871501012102f541
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>