[BUG] waagent missing ipv6.addr-gen-mode eui64 from nmcli command

Running **sudo waagent -deprovision+user** and I got this error:

_ERROR MainThread Command: [nmcli device modify eth0 ipv4.dhcp-hostname localhost.localdomain ipv6.dhcp-hostname localhost.localdomain], return code: [6], result: [Error: Reapplying connection to device 'eth0' (/org/freedesktop/NetworkManager/Devices/2) failed: The settings specified are invalid: ipv6.addr-gen-mode: property is invalid_

The fix is to do the following:

Run

$ _nmcli device modify eth0 ipv4.dhcp-hostname localhost.localdomain ipv6.dhcp-hostname localhost.localdomain **ipv6.addr-gen-mode eui64**_

before

running _sudo waagent deprovision_

Distro: **RHEL8.7**
_WALinuxAgent version: 2.7.0.6 running on redhat 8.7
Python: 3.6.8_

**Additional context**
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**Log file attached**
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