Move ipv6 config option into network-feature-enabled

This commit moves the ipv6 option into the proper config group.
Previously, there was an ipv6_enabled option under the network group.
This was the incorrect location for this type of option since, ipv6
is an optional feature it should be in the feature enabled group.

Change-Id: I35769cf4d18363fad56ed5150b4d01d8a5ad17e7
Merge "Move ipv6 config option into network-feature-enabled"