[ofono] Handle gril ioconnection shutdown by exit

Before: gril connection hand up (G_IO_HUP) causes ofono gril
to shutdown and no messages are handled.
After: gril notifies ril plugin which emits a message
to clients and exits ofono.

Signed-off-by: Tommi Kenakkala <tommi.kenakkala@oss.tieto.com>
[rilmodem] Do not close the ofono if rild dies

There is no need to kill ofono if connection to rild dies. We just
need to inform client about connection drop and try again

Signed-off-by: Jussi Kangas <jussi.kangas@oss.tieto.com>