BUG/MINOR: tools: fix set_net_port() / set_host_port() on IPv4

BUG/MINOR: tools: fix set_net_port() / set_host_port() on IPv4

These two functions were apparently written on the same model as their
parents when added by commit 11bcb6c4f ("[MEDIUM] IPv6 support for syslog")
except that they perform an assignment instead of a return, and as a
result fall through the next case where the assigned value may possibly
be partially overwritten. At least under Linux the port offset is the
same in both sockaddr_in and sockaddr_in6 so the value is written twice
without side effects.

This needs to be backported as far as 1.5.