Make NextHopIpAddress an optional parameter.

Author: Ed Munoz

src/ServiceManagement/Network/Commands.Network/Routes/SetAzureRoute.cs

@@ -32,7 +32,7 @@ public class SetAzureRoute : NetworkCmdletBase
         [Parameter(Position = 3, Mandatory = true, HelpMessage = "The new route's next hop type. Valid values are \"VPNGateway\".")]
         public string NextHopType { get; set; }
 
-        [Parameter(Position = 4, Mandatory = true, HelpMessage = "The new route's next hop ip address." +
+        [Parameter(Position = 4, Mandatory = false, HelpMessage = "The new route's next hop ip address." +
                                                                  " This parameter can only be specifide for \"VirtualAppliance\" next hops.")]
         public string NextHopIpAddress { get; set; }