The whole idea is run ESXi in a VM in Azure IaaS, where I cannot use legacy NIC ...
I'm not really sure where you are going with this. Hyper-V doesn't virtualize the hardware-assisted virtualization features of the physical processor, so you would be stuck running 32-bit nested guests with binary translation. Performance would be terrible. Moreover, unless you can set your NIC to promiscuous mode, you wouldn't be able to get networking through to your nested VMs.
Now that Windows 10 and Server 2016 support nested virtualisation, is anyone working on porting the native hyper-v Network adapter drivers to ESXi so we're not limited to 100mbit on the legacy adapter?
having the same problem hope some IT genius get a solution to this problem cheers