IPv6 support

[codefromthecrypt]

We currently support logging of only IPv4 addresses. Starting with Zipkin 1.4 endpoints can omit IPv4 (by setting Endpoint.ipv4 to 0), and optionally log Endpoint.ipv6 as the raw 16byte address.
https://github.com/openzipkin/zipkin-api/blob/master/thrift/zipkinCore.thrift#L276

In json, both are the string formatting http://zipkin.io/zipkin-api

ipv4:
string
The text representation of a IPv4 address associated with this endpoint. Ex. 192.168.99.100
ipv6:
string
The text representation of a IPv6 address associated with this endpoint. Ex. 2001:db8::c001

[jcarres-mdsol]

Made it an enhancement.
@bvillanueva-mdsol @lschreck-mdsol @kenyamat FYI