bgpd, zebra: rfc-5549-generic.patch

bgpd, zebra: rfc-5549-generic.patch

This adds support for BGP RFC 5549 (Extended Next Hop Encoding capability)

     * send and receive of the capability
     * processing of IPv4->IPv6 next-hops
     * for resolving these IPv6 next-hops, itsworks with the current
       next-hop-tracking support
     * added a new message type between BGP and Zebra for such route
       install/uninstall
     * zserv side of changes to process IPv4 prefix ->IPv6 next-hops
     * required show command changes for IPv4 prefix having IPv6 next-hops

Few points to note about the implementation:

     * It does an implicit next-hop-self when a [IPv4 prefix -> IPv6 LL next-hop]
       is to be considered for advertisement to IPv4 peering (or IPv6 peering
       without Extended next-hop capability negotiated)

     * Currently feature is off by default, enable it by configuring
       'neighbor <> capability extended-nexthop'

     * Current support is for IPv4 Unicast prefixes only.

IMPORTANT NOTE:

     This patch alone isn't enough to have IPv4->IPv6 routes installed into
     the kernel. A separate patch is needed for that to work for the netlink
     interface.

Signed-off-by: Vipin Kumar <vipin@cumulusnetworks.com>
Reviewed-by: Daniel Walton <dwalton@cumulusnetworks.com>
             Vivek Venkatraman <vivek@cumulusnetworks.com>
             Donald Sharp <sharpd@cumulusnetworks.com>