The routing table (in its current) form should not be used to make
decisions about whether a remote address is a broadcast address or
not (for IPv4).
Note, a destination subnet does not always map to a network.
E.g. RouterA may have a route to 192.168.0.0/22 through RouterB,
but RouterB may be configured with 4x /24 subnets on 4 different
interfaces.
See https://github.com/google/gvisor/issues/3938.
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