tests: don't assume IPv4 only in remote addr tests

Tests in test-net-remote-address-port.js assume that client and server
sockets always use IPv4. However, depending on the OS and the network
interfaces setup, this is not true. This change makes the test consider
that both IPv4 or IPv6 sockets are valid.

Tested on OS X, SmartOS, Ubuntu and Windows 7.

Fixes #8096.