When rendering the routename() or netname() of a struct sockaddr

When rendering the routename() or netname() of a struct sockaddr
with an unknown address family, use a more straightforward loop
for dumping the contents of sa_data as hex:

- start at sa_data, end at sa + sa_len (NOT sa_data + sa_len);
- don't make assumptions about the size of u_short.

Inspired-by-patch-by: Sepherosa Ziehau <sepherosa_at_softhome_dot_net>