Fails to parse IPv6 addresses in configuration

[djs55]

@dsheets reports that this error appears:

com.docker.slirp: [ERROR] failed to parse com.docker.driver.amd64-linux/slirp/dns: Failed to parse configuration: Ipaddr.Parse_error("invalid character ':' at 4", "2001:8b0:cb40:3495:3291:8fff:fe02:8cde")

We should use Ipaddr.of_string to parse IPv4 and v6 addresses. Probably the only annoying thing is the specification of the port. Perhaps we should use a separate line for that, rather than stick it on the end of the IP address? Some people use [addr]:port also there exist v6 zones like addr%iface. A newline might be the best terminator.

References:

• https://tools.ietf.org/html/rfc5952#section-6

[djs55]

Seen in https://github.com/docker/for-mac/issues/1337