ipv6 related improvements

Fix so the socket address structures common fields (most importantly the address family) align.
So we can correctly check the address family which ever socket address structure we are working with/casting to.
http://beej.us/guide/bgnet/output/html/multipage/sockaddr_inman.html

The additional JS C defines are for completeness and for the node sockets library: https://github.com/mnaamani/enet-emscripten/blob/master/src/library_node_sockets.js#L280

I ran tests/runner.py before and after the chagnes.
The same tests fail on the incoming branch. No additional tests fail with the new commits.
test_gethostbyname
test_crunch
test_llvm_nativizer