Use vxlan for inner flannel

[rkoster]

Since the flannel udp backend is only supposed to be used for debug purposes investigate what it takes to switch to vxlan.

So far we have performed the following tests

outer   inner   bosh  k8s
vxlan   udp     works works
vxlan   vxlan   works !cross-node only ping
vxlan   host-gw works !cross-node
udp     udp     works ?
host-gw vxlan   !cross-node (tested on was)

Which show vxlan vxlan is closest to working (at least works cross az).

We observed the following behaviour
accessing coredns via cluster ip only works sometimes (probably when it routes to the same zone):

ping works across all zones:

nc can connect but dig does not work: