Taking first interface address in hostgw instead of the last one - required for kube-proxy in userspace

[ptylenda]

NOTE: this pull request is for your gonetsh vendor package - I am not sure how currently the packages should be maintained, treat this pull request more like a "issue report and workaround"

When kubeproxy is running in userspace mode, it will attach multiple interfaces for services to cbr0 interface like below:

Configuration for interface "vEthernet (nat)"
    DHCP enabled:                         Yes
    IP Address:                           172.17.32.1
    Subnet Prefix:                        172.17.32.0/20 (mask 255.255.240.0)
    InterfaceMetric:                      15

Configuration for interface "vEthernet (Ethernet)"
    DHCP enabled:                         Yes
    IP Address:                           172.28.1.208
    Subnet Prefix:                        172.28.1.0/23 (mask 255.255.254.0)
    Default Gateway:                      172.28.1.1
    Gateway Metric:                       0
    InterfaceMetric:                      25

Configuration for interface "vEthernet (cbr0_ep)"
    DHCP enabled:                         No
    IP Address:                           10.200.9.2
    Subnet Prefix:                        10.200.9.0/24 (mask 255.255.255.0)
    IP Address:                           10.201.0.1
    Subnet Prefix:                        10.0.0.0/8 (mask 255.0.0.0)
    IP Address:                           10.201.0.10
    Subnet Prefix:                        10.0.0.0/8 (mask 255.0.0.0)
    IP Address:                           10.201.39.237
    Subnet Prefix:                        10.0.0.0/8 (mask 255.0.0.0)
    Default Gateway:                      10.200.9.1
    Gateway Metric:                       256
    InterfaceMetric:                      25

Configuration for interface "Loopback Pseudo-Interface 1"
    DHCP enabled:                         No
    IP Address:                           127.0.0.1
    Subnet Prefix:                        127.0.0.0/8 (mask 255.0.0.0)
    InterfaceMetric:                      75

Current implementation of flannel hostgw backed for windows will result then in:

I0304 03:10:55.183836   10116 hostgw_windows.go:197] Attached bridge endpoint [cbr0_ep] to host
I0304 03:10:55.411837   10116 hostgw_windows.go:211] Enabled forwarding on [vEthernet (Ethernet)] index [7]
E0304 03:10:55.543839   10116 main.go:285] Error registering network: unable to find interface for IP Addess [10.200.9.2], error: Interface not found: 10.200.9.2
I0304 03:10:55.544849   10116 main.go:338] Stopping shutdownHandler...

This is caused by the fact, that the last IP ("10.201.39.237") for cbr0 will be taken as main interface IP instead of "10.200.9.2".

The pull request fixes this issue by not overwriting IP, subnet and gateway if they are already resolved, there is a probably better way to do this using pure netsh commands, but I am not an expert in this manner.

[rakelkar]

@Dingov @madhanrm FYI