[tests] Adjust test to work in unsupported scenarios

[tests] Adjust test to work in unsupported scenarios

On Android (possibly on other systems too) it is possible that no gateway address is available and its lack is NOT an error
Here is a sample of /proc/net/route from Nexus 9 running Android 5.1.1 (IPInterfaceProperties parses that file on Linux)

  Iface	Destination	Gateway 	Flags	RefCnt	Use	Metric	Mask		MTU	Window	IRTT
  wlan0	0001A8C0	00000000	0001	0	0	0	00FFFFFF	0	0	0

Gateway is set to any address and it is explicitly ignored by the route information parser

For comparison, here's route contents from an Android 4.4.4 device:

  Iface	Destination	Gateway 	Flags	RefCnt	Use	Metric	Mask		MTU	Window	IRTT
  wlan0	00000000	0101A8C0	0003	0	0	0	00000000	0	0	0
  wlan0	00000000	0101A8C0	0003	0	0	203	00000000	0	0	0
  wlan0	0001A8C0	00000000	0001	0	0	0	00FFFFFF	0	0	0
  wlan0	0001A8C0	00000000	0001	0	0	0	00FFFFFF	0	0	0
  wlan0	0001A8C0	00000000	0001	0	0	203	00FFFFFF	0	0	0
  wlan0	0101A8C0	00000000	0005	0	0	0	FFFFFFFF	0	0	0

Obviously, this test fails on the first device and succeeds on the second. For this reason the test is modified to succeed
in case of devices like the first one since it's not a real failure but a shortcoming of the .NET API