How to force DHCP renew?

[Stephen Hemminger <stephen networkplumber org>]

On Azure (and probably other VM environments), there is a desire to cause guest VM to renew DHCP
lease in response to host infrastructure changes. These include things like spinning up
lots of VM's then suspending them and later unfreezing them as needed. The other scenario
is doing renew following migration.

The current kernel code has a hack to try and simulate link bounce, but it doesn't
work very well and the old ISC DHCP client does nothing. Network manager might be
able to do something better??