Use free_known_addresses() to free memory allocated by get_known_addresses().

Use free_known_addresses() to free memory allocated by get_known_addresses().

We know what struct addrinfo looks like, but the standard says nothing about
how it is allocated. So we cannot trust freeaddrinfo() to work correctly on
the struct addrinfo list we allocated ourselves in get_known_addresses().
To make a distinction by allocations from the latter and from str2addrinfo(),
we keep two pointers (*ai and *aip) in struct outgoing, and use the freeing
function that is appropriate for each.