Simplify DPDK integration with provider network

[EmilienM]

Re-use hostonly provider network when DPDK is enabled and instead of adding a dummy interface (dummy1), just use the physical interface that we want to use for DPDK.

This will avoid confusions when our users see multiple provider networks. In fact, one is enough and should be used.

Note: we maintain the SRIOV provider network separated, since it's using another kind of interface etc.

[EmilienM]

@mdbooth for review, please

[EmilienM]

I'm currently testing it. /hold

[EmilienM]

I tested it and it worked fine.

[adduarte]

This will help quite a bit. /lgtm