initalize the global_opts.af_hint to AF_INET or systems such as Linux that
have a native getaddrinfo() because they support IPv6 will attempt to
create IPv6 sockets.  This brings up a problem with the new global_opts
structure; in order to initialize them to a value other than 0, we need to
explicitly initialize them all in an order that matches the order in
rsync.h.  I think that's more inconvenient & error prone than keeping
global variables.