iproute: properly support high routing table IDs

iproute: properly support high routing table IDs

The Linux kernel uses two distinct fields to denote the routing table ID in
use by network routes; the 8 bit `rtm_table` member of `struct rtmsg` and the
32 bit `RTA_TABLE` netlink attribute.

If a routing table ID is larger than 255, the `RT_TABLE` attribute must be used
and the `rtm_table` field has to be set to the special `RT_TABLE_UNSPEC` value.

This commit adds a patch which...
 - switches the *_n2a() and *_a2n() functions of rt_names.c to use dynamically
   sized, name-sorted arrays instead of fixed arrays limited to 1024 slots in
   order to support IDs up to 65535
 - adds proper handling of high table IDs to iprule.c and iproute.c when
   adding, removing and dumping ip rules and network routes

After this change, the Busybox ip applet fully supports IP rules with high ID
numbers, using the same logic as the full iproute2.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>