Currently, in notify_send_and_recv function, pupnp waits for
HTTP_DEFAULT_TIMEOUT seconds when trying to send a GENA notification.
When there is a lot of notifications with CPs which was disconnected
without unsusbcribing, all the pupnp threads are blocked on this
timeout. To correct, this issue, this patch adds a new variable,
GENA_NOTIFICATION_SENDING_TIMEOUT, which can be used to lower the
timeout so GENA threads return quickly when writing is impossible. By
the same mean, pupnp waits the CP's answer to the NOTIFY for
HTTP_DEFAULT_TIMEOUT seconds, so this patch adds a new variable,
GENA_NOTIFICATION_ANSWERING_TIMEOUT, to customize this value.
(cherry picked from commit e6c548f57a26ef5e681135cf34ea780b95209be8)
b0cab00ca3