Add support for larger number of routing tables

Add support for larger number of routing tables

[IPROUTE]: Add support for larger number of routing tables

Support support for 2^32 routing tables by using the new RTA_TABLE
attribute for specifying tables > 255 and intepreting it if it is
sent by the kernel.

When tables > 255 are used on a kernel not supporting it an error will
occur because of the unknown netlink attribute.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>