*: Consistently support 32-bit route tags

*: Consistently support 32-bit route tags

This patch improves zebra,ripd,ripngd,ospfd and bgpd so that they can
make use of 32-bit route tags in the case of zebra,ospf,bgp or 16-bit
route-tags in the case of ripd,ripngd.

It is based on the following patch:

    commit d25764028829a3a30cdbabe85f32408a63cccadf
    Author: Paul Jakma <paul.jakma@hpe.com>
    Date:   Fri Jul 1 14:23:45 2016 +0100

    *: Widen width of Zserv routing tag field.

But also contains the changes which make this actually useful for all
the daemons.

Signed-off-by: Christian Franke <chris@opensourcerouting.org>