ipv4: Fix selected source address for next hops added to groups with no gateway

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2189195 Upstream Status: linux.git Omitted-fix:

• e5ec6a251338 ("mlxsw: spectrum_router: Fix IPv4 nexthop gateway indication"): Already included in Centos Stream 9.

The real fix is patch 6, but the upstream history is a bit messy: Patch 1 (original fix) needed an additional fix (patch 3), but both finally got reverted (patches 4 and 5).

The reasons for backporting the full history are:

• Prevent automatic tools from complaining about missing fixes.

• Backport the kernel selftest found in the original patch series (see patch 2).

• Keep the explanations found in the commit message of the original fix.

Detailed explanations about the shortcomings of patch 1 can be found at https://lore.kernel.org/netdev/6c8a44ba-c2d5-cdf-c5c7-5baf97cba38@ssi.bg/

Signed-off-by: Guillaume Nault gnault@redhat.com