tcp: Rack not being very friendly with V6:4 socket and having a connection from V4

[rrs]

Summary

There were two bugs that prevented V4 sockets from connecting to
a rack server running a V4/V6 socket. As well as a bug that stops the
mapped v4 in V6 address from working.

This fix addresses each bug.

Test Plan

make sure that a simple server and client running the different permutations works i.e.

V4-6 socket on server
client server
V6 ->
V4 ->
V4MappedV6 ->