Merge branch 'net-mctp-add-support-for-gateway-routing'

Jeremy Kerr says:

====================
net: mctp: Add support for gateway routing

This series adds a gateway route type for the MCTP core, allowing
non-local EIDs as the match for a route.

Example setup using the mctp tools:

    mctp route add 9 via mctpi2c0
    mctp neigh add 9 dev mctpi2c0 lladdr 0x1d
    mctp route add 10 gw 9

- will route packets to eid 10 through mctpi2c0, using a dest lladdr
of 0x1d (ie, that of the directly-attached eid 9).

The core change to support this is the introduction of a struct
mctp_dst, which represents the result of a route lookup. Since this
involves a bit of surgery through the routing code, we add a few tests
along the way.

We're introducing an ABI change in the new RTM_{NEW,GET,DEL}ROUTE
netlink formats, with the support for a RTA_GATEWAY attribute. Because
we need a network ID specified to fully-qualify a gateway EID, the
RTA_GATEWAY attribute carries the (net, eid) tuple in full:

    struct mctp_fq_addr {
        unsigned int net;
        mctp_eid_t eid;
    }

Of course, any questions, comments etc are most welcome.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
====================

Link: https://patch.msgid.link/20250702-dev-forwarding-v5-0-1468191da8a4@codeconstruct.com.au
Signed-off-by: Paolo Abeni <pabeni@redhat.com>