REDIRECT in the OUTPUT chain rewrites the destination to 127.0.0.1,
then ip_route_me_harder() reroutes with the socket's bound interface
constraint (flowi4_oif). Since 127.0.0.1 is only reachable via lo,
the routing lookup fails and the packet is silently dropped.
Add a fallback routing table with `local 127.0.0.1` entries for each
non-loopback interface. When the local table lookup fails due to OIF
mismatch, the fallback table provides a matching RTN_LOCAL route.
The kernel then overrides dev_out to loopback (route.c:2857), so the
packet is delivered locally to the redirect server as intended.
This fixes NetworkManager connectivity checks and other tools that
use SO_BINDTODEVICE (e.g. curl --interface).
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