[package] add package for BIRD Internet Routing Daemon

[package] add package for BIRD Internet Routing Daemon

Here is the patch that adds a package for The BIRD Internet Routing
Daemon. It is updated to the current version of BIRD (v 1.2.2).

BIRD is an internet routing daemon that implements OSPF, RIP and BGP.
It is fast, lightweight and small (cca 300 kB), therefore ideal for
OpenWRT based routers.

The makefile is rather tricky, as BIRD have to be built two times  (for
IPv4 and IPv6 versions) and there are separate packages for BIRD daemon
and BIRD client, because client depends on libreadline and is not
strictly necessary.

Signed-off-by: Ondrej Zajicek <santiago@crfreenet.org>
git-svn-id: svn://svn.openwrt.org/openwrt/packages@20780 3c298f89-4303-0410-b956-a3cf2f4a3e73