The short, technically dlightly incorrect answer is you cant do this.
The long answer is -
You cant take 1 gigabit port and connect it to 2 gigabit ports and get high speed - in fact the best you would get is 100 megabits on 1 of the 2 ports.
You have not stated the speed.of your Internet connection but unless you are purchasing > gigabit from your ISP - which is vanishingly unlikely, increasing the speed between your vios router and x10 wont help because thats not the bottleneck.
I dont know what VIOS hardware is, but if you are truly getting > gig speeds, you could theoretically turn 1 of your X10 ethernet ports into a WAN port and then have 2 wan connections. This is very hard to set up and will come with lots of limitations unless the VIOS box does link aggregation, in which case its just very hard.
If your connection is not performing as well as it shoiuld be you should focus on finding and fixing the bottleneck, whivh is unlikrly to be between the VIOS and X10 box unless you have a faulty ethernet cable.