netdev-windows: Add ARP lookup and next hop functionality.

netdev-windows: Add ARP lookup and next hop functionality.

This patch implements two functionalities needed for an active manager:
1. ARP lookup
2. Next hop

The first uses the Windows GetIpNetTable() function:
https://msdn.microsoft.com/en-us/library/windows/desktop/aa365956%28v=vs.85%29.aspx

The second one uses GetAdaptersAddresses() function:
https://msdn.microsoft.com/en-us/library/windows/desktop/aa365915%28v=vs.85%29.aspx

Both API's are found in the Iphlpapi library. We need to add this library when compiling.

Documentation and appveyor config has been updated to match the use of the new library.

Tested using opendaylight.

Signed-off-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Reported-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Reported-at: https://github.com/openvswitch/ovs-issues/issues/63
Acked-by: Eitan Eliahu <eliahue@vmware.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>