adsl: settings and initial "scaffolding"

This patch adds the settings code (NMSettingAdsl) and the initial
"scaffolding" i.e., a tiny stub version of NMDeviceAdsl and the
udev handler code to get the device detected.

With this patch you should be able to see an atm device being detected
by networkmanager in the logs, although of course it doesn't
do anything useful yet.

Extract from the logs:

 [1304668252.341354] [nm-udev-manager.c:562] adsl_add(): adsl_add: ATM Device detected from udev. Adding ..
(ueagle-atm0): failed to look up interface index
(ueagle-atm0): new ADSL device (driver: 'ueagle-atm' ifindex: -1)
(ueagle-atm0): exported as /org/freedesktop/NetworkManager/Devices/2
(ueagle-atm0): now managed
(ueagle-atm0): device state change: unmanaged -> unavailable (reason 'managed') [10 20 2]
(ueagle-atm0): deactivating device (reason: 2).
 [1304668252.345102] [nm-system.c:1349] flush_routes(): (ueagle-atm0) failed to lookup interface index
 [1304668252.347821] [nm-device.c:3912] nm_device_state_changed(): (ueagle-atm0): device is available,

In this version, we hack the nm-device.c:nm_device_get_priority() to get better priority
instead of changing the DeviceType enum.

Signed-off-by: Pantelis Koukousoulas <pktoss@gmail.com>

include/NetworkManager.h

@@ -107,6 +107,7 @@ typedef enum {
  * GSM/UMTS, or LTE network access protocols
  * @NM_DEVICE_TYPE_INFINIBAND: an IP-over-InfiniBand device
  * @NM_DEVICE_TYPE_BOND: a bond master interface
+ * @NM_DEVICE_TYPE_ADSL: ADSL modem
  *
  * #NMDeviceType values indicate the type of hardware represented by
  * an #NMDevice.
@@ -124,6 +125,7 @@ typedef enum {
 	NM_DEVICE_TYPE_INFINIBAND = 9,
 	NM_DEVICE_TYPE_BOND       = 10,
 	NM_DEVICE_TYPE_VLAN       = 11,
+	NM_DEVICE_TYPE_ADSL       = 12,
 } NMDeviceType;
 
 /**