Request to improve updateNetwork api

##### ISSUE TYPE

* Improvement Request / Future request

##### COMPONENT NAME

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API
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##### CLOUDSTACK VERSION

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4.18.1.0
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##### CONFIGURATION

N/A
##### OS / ENVIRONMENT

N/A

##### SUMMARY

Request to improve updateNetwork api to add/change ipv6 CIRD, ipv6 gate, ipv6 end ,start ip, router ipv6.

##### STEPS TO REPRODUCE

Create ipv4 only guest network. Try to add ipv6 CIDR, gateway, start ip, end ip.

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##### EXPECTED RESULTS

Possibility to change the settings described above using the interface or api
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##### ACTUAL RESULTS

You won't be able to do this either through the interface or the api

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Start with the updateNetwork API entry point and reproduce the request against an IPv4-only guest network. Determine the intended behavior for changing the IPv6 CIDR, gateway, start and end IPs, and router IPv6 through both the API and interface. Done means those settings can be changed successfully through the requested paths.

Written by the indexing model from the issue text.