net: family option in net.connect

`dns.lookup` defaults to selecting IPv4 record even if IPv6 is available
for the desired zone. Generally, this approach works, but if IPv4
address is unavailable - there'll be no other way to opt-out and connect using
IPv6 address than calling `dns.lookup` and passing it to `.connect()`
directly.

This commit adds `family` option to `net.connect` method to figure out
this issue.