Introduce tcp_connect().

Introduce tcp_connect().

This replaces get_host_info(). The two callers of the latter,
client_connect() and http_recv_open(), did exactly the same, namely
initializing a struct sockaddr_in which was then used for PARA_CONNECT().

So move this common code to tcp_connect(). Additional benefit of this
is that the only remaining callers of init_sockaddr() are in net.c, so
make this function static.