sd-dhcp6: fix domainname memleak

strv_extend() does not consume the passed entry, hence, we must properly
free it. Furthermore, we should *not* use strv_consume() as we do greedy
allocations on 'ret'; and greedy-allocations should only be used for short
lived objects or caches.

Fix the domainname parser to properly free temporary storage when done.

src/libsystemd-network/dhcp6-option.c

@@ -405,7 +405,6 @@ int dhcp6_option_parse_domainname(const uint8_t *optval, uint16_t optlen,
                 if (r < 0)
                         goto fail;
 
-                ret = NULL;
                 idx++;
         }