Add support for ipv6 tethering stats

Requirement: Support for ipv6 tethering stats

Current implementation does not have support
for calculating the Ipv6 tethering  traffic

Solution:
Parse the ipv6 tether counter chains output
Update the output data to NetworkManagementService

Change-Id: I7d626b5697f5aa07c0266032a07be8f70a17f4e3
CRs-Fixed: 690173