Use the defined access method for structure.

Not all struct sockaddr are going to have the sa_family as their first field.
Since there is a named structure member, we can simply use that and let
the compiler sort it out.

This fixes a bug with at least FreeBSD and allows us to remove the
special case for Apple.

src/wire.c

@@ -687,11 +687,8 @@ int fill_sockaddr (struct sockaddr * addr,
 // fills struct sockaddr's data into n2n_sock
 int fill_n2nsock (n2n_sock_t* sock, const struct sockaddr* sa) {
 
-#ifdef __APPLE__
     sock->family = sa->sa_family;
-#else
-    sock->family = *(sa_family_t*)sa;
-#endif
+
     switch(sock->family) {
         case AF_INET: {
             sock->port = ntohs(((struct sockaddr_in*)sa)->sin_port);